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An Amphibious Whale from the Middle Eocene of Peru Reveals Early South Pacific Dispersal of Quadrupedal Cetaceans
Abstract
Cetaceans originated in south Asia more than 50 million years ago (mya), from a small quadrupedal artiodactyl ancestor [1-3]. Amphibious whales gradually dispersed westward along North Africa and arrived in North America before 41.2 mya [4]. However, fossil evidence on when, through which pathway, and under which locomotion abilities these early whales reached the New World is fragmentary and contentious [5-7]. Peregocetus pacificus gen. et sp. nov. is a new protocetid cetacean discovered in middle Eocene (42.6 mya) marine deposits of coastal Peru, which constitutes the first indisputable quadrupedal whale record from the Pacific Ocean and the Southern Hemisphere. Preserving the mandibles and most of the postcranial skeleton, this unique four-limbed whale bore caudal vertebrae with bifurcated and anteroposteriorly expanded transverse processes, like those of beavers and otters, suggesting a significant contribution of the tail during swimming. The fore- and hind-limb proportions roughly similar to geologically older quadrupedal whales from India and Pakistan, the pelvis being firmly attached to the sacrum, an insertion fossa for the round ligament on the femur, and the retention of small hooves with a flat anteroventral tip at fingers and toes indicate that Peregocetus was still capable of standing and even walking on land. This new record from the southeastern Pacific demonstrates that early quadrupedal whales crossed the South Atlantic and nearly attained a circum-equatorial distribution with a combination of terrestrial and aquatic locomotion abilities less than 10 million years after their origin and probably before a northward dispersal toward higher North American latitudes. VIDEO ABSTRACT.
... The Protocetidae is a diverse paraphyletic family of archaic whales that constitute a major step in the evolutionary transition from land mammals to fully aquatic cetaceans (Gingerich et al., 2009;Bianucci and Gingerich, 2011). Protocetids were all quadrupedal swimmers but displayed diverse locomotor lifestyles from the amphibious basal forms to fully pelagic species (Buchholtz, 1998(Buchholtz, , 2007Hulbert, 1998;Luo and Gingerich, 1999;Gingerich, 2010;Gao and Ni, 2015;Bebej and Smith, 2017;Gingerich et al., 2019;Vautrin et al., 2020), and thanks to their inferred osmoregulatory capabilities (Clementz et al., 2006), were capable of crossing vast oceanic areas (Lambert et al., 2019). From their cradle in Pakistan, the group rapidly dispersed westward through the Tethys Seaway (Wang et al., 2002;Fordyce, 2018) to colonize most of the oceans of the planet in only a few million years from the early to the late Lutetian (Lambert et al., 2019). ...
... Protocetids were all quadrupedal swimmers but displayed diverse locomotor lifestyles from the amphibious basal forms to fully pelagic species (Buchholtz, 1998(Buchholtz, , 2007Hulbert, 1998;Luo and Gingerich, 1999;Gingerich, 2010;Gao and Ni, 2015;Bebej and Smith, 2017;Gingerich et al., 2019;Vautrin et al., 2020), and thanks to their inferred osmoregulatory capabilities (Clementz et al., 2006), were capable of crossing vast oceanic areas (Lambert et al., 2019). From their cradle in Pakistan, the group rapidly dispersed westward through the Tethys Seaway (Wang et al., 2002;Fordyce, 2018) to colonize most of the oceans of the planet in only a few million years from the early to the late Lutetian (Lambert et al., 2019). Although originating from Asia, the family name was coined based on early African discoveries (Stromer, 1908), following the description of Protocetus atavus from the middle Eocene Mokattam Formation in Egypt (Fraas, 1904). ...
... A matrix of 167 characters and 45 taxa has been assembled to assess the phylogenetic position of the new Togolese specimen. The core of this matrix is based on Geisler et al. (2005), and Gol'din and Zvonok (2013) supplemented with one additional character from Thewissen and Hussain (2000), one from Bianucci and Gingerich (2011), (20) from Mourlam and Orliac (2018), two from Gibson et al. (2019), two from Lambert et al. (2019) and (22) from Vautrin et al. (2020). Among them, 15 characters have been modified and/or split into new ones (see characters 2, 9, 10, 20, 30, 31, 45, 46, 53, 75, 87-92, 94, 116 and 124; see also Supplementary Text 1). ...
... Nevertheless, by possessing large supraorbital processes, protocetids resemble more derived cetaceans, such as basilosaurids and early members of Neoceti [5]. Protocetidae emerged during the early middle Eocene in the Indo-Pakistan region, where they rapidly diversified and dispersed to other parts of the world [6][7][8][9][10]. Protocetidae initially included Protocetus and Eocetus from the middle Eocene of Egypt [11], but with more recent discoveries has expanded into a large paraphyletic family of archaeocetes that includes three subfamilies: Protocetinae, Makaracetinae, and Georgiacetinae [12]. ...
... We coded Phiomicetus into the matrix of Lambert et al. [9], supplemented with additional taxa, characters, and some coding modifications (see electronic supplementary material, data). With the addition of Phiomicetus, the updated matrix includes 44 taxa and 190 characters, with 39 ordered characters. ...
... Phylogenetic analysis of our data matrix using Bayesian tip-dating analysis and FBD parameterization (figure 2; electronic supplementary material) recovered Protocetidae as paraphyletic. This consensus configuration is similar to what has been found in previous studies [9,25]. The Bayesian tip-dating analysis confirms that the most basal protocetids are the Indo-Pakistani protocetids Maiacetus, Artiocetus, and Rodhocetus, followed by sequentially more crownward genera. ...
Over about 10 million years, the ancestors of whales transformed from herbivorous, deer-like, terrestrial mammals into carnivorous and fully aquatic cetaceans. Protocetids are Eocene whales that represent a unique semiaquatic stage in that dramatic evolutionary transformation. Here, we report on a new medium-sized protocetid, Phiomicetus anubis gen. et sp. nov., consisting of a partial skeleton from the middle Eocene (Lutetian) of the Fayum Depression in Egypt. The new species differs from other protocetids in having large, elongated temporal fossae, anteriorly placed pterygoids, elongated parietals, an unfused mandibular symphysis that terminates at the level of P3, and a relatively enlarged I3. Unique features of the skull and mandible suggest a capacity for more efficient oral mechanical processing than the typical protocetid condition, thereby allowing for a strong raptorial feeding style. Phylogenetic analysis nests Phiomicetus within the paraphyletic Protocetidae, as the most basal protocetid known from Africa. Recovery of Phiomicetus from the same bed that yielded the remingtonocetid Rayanistes afer provides the first clear evidence for the co-occurrence of the basal cetacean families Remingtonocetidae and Protocetidae in Africa. The discovery of Phiomicetus further augments our understanding of the biogeography and feeding ecology of early whales.
... The Eocene-Miocene deposits of the East Pisco Basin, southern Peru, feature exceptionally common and remarkably well-preserved marine vertebrate remains that make them a true Fossil Lagerstätte (Bosio et al., 2021a,b;Esperante et al., 2015;Gariboldi et al., 2015). Fossils from the East Pisco Basin include marine mammals, seabirds, marine reptiles, and fishes (Bianucci et al., , 2016c(Bianucci et al., , 2020Clarke et al., 2007;Clarke et al., 2010;Collareta et al., 2015Collareta et al., , 2017Collareta et al., , 2020aCollareta et al., , 2020bde Muizon et al., 2019;Gioncada et al., 2016Gioncada et al., , 2018Lambert et al., 2015Lambert et al., , 2018Lambert et al., , 2017Lambert et al., , 2019Lambert et al., , 2020aLambert et al., , 2020bLandini et al., 2017aLandini et al., , 2017bLandini et al., , 2019Marx et al., 2017). ...
... The Paleogene strata from which these outstanding fossil records were obtained, have been described for some localities of the Pisco Basin and sparsely dated via 39 Ar-40 Ar dating (DeVries, 1998;Uhen et al., 2011), as well as by biostratigraphic data on their radiolarians, diatoms, calcareous nannofossils and foraminifera (Coletti et al., 2019;DeVries, 1998;DeVries et al., 2006;Dunbar et al., 1990;Fourtanier and Macharé, 1988;Ibaraki, 1993;Lambert et al., 2019;Lambert et al., 2017;Marty, 1989;Tsuchi et al., 1992;Tsuchi et al., 1988). Nonetheless, a thorough biostratigraphic assessment of these sediment units is at present still lacking. ...
... Although several biostratigraphic studies have been performed for the East Pisco Basin Eocene sediments, by means of calcareous nannofossils, diatoms, planktonic foraminifera and radiolarians Tsuchi et al., 1992;Tsuchi et al., 1988;Ibaraki, 1993;DeVries, 1998), and often resulting in the recognition of biozones, only a few stratigraphic columns have been analysed in detail, with the identification of bioevents. Among these, Lambert et al. (2017Lambert et al. ( , 2019 Eocene calcareous nannofossils along the stratigraphic columns analysed in this work are dominated by large placoliths, with low diversity. Many species representing stratigraphic markers are rare (R. erbae, C. grandis, C. oamaruensis, S. spiniger, D. saipanensis, D. barbadiensis) or absent (R. isabellae, some Sphenolithus species), thus preventing the full application of the high-resolution biostratigraphic scheme developed by Agnini et al. (2014) for low and middle latitudes. ...
The Eocene sediment successions of the East Pisco Basin (southern Peru) host an exceptionally rich and well-preserved assemblage of vertebrate fossils. However, due to the dearth of geochronological and biostratigraphic controls as well as of stratigraphic correlations, our understanding of these rocks and their fossil content remains elusive.
This paper provides a comprehensive calcareous nannofossil, diatom, and silicoflagellate biostratigraphic framework for the Eocene strata exposed at four localities along the Ica River Valley, permitting a robust chronological calibration of the marine vertebrate fauna entombed therein and a better definition of important appearance/ extinction events. The Paracas Formation, deposited directly on top of the Proterozoic and Paleozoic rocks of the crystalline basement, is formed by a siliciclastic-bioclastic gravel-sized deposit (Los Choros member) and calcareous-terrigenous siltstone (Yumaque member) that was deposited from the Lutetian (47.8–41.2 Ma) through the Bartonian (41.2–37.7 Ma) to the early Priabonian (37.7–33.9 Ma). The unconformably overlying Otuma Formation consists of a basal sand, followed by calcareous siltstone intercalated by diatomite layers towards the top. In the study area, the Otuma Formation is Priabonian in age and is truncated at the top by an unconformity at the base of the overlying Miocene Chilcatay Formation. Due to the angular nature of the unconformity, the upper Otuma strata reach the Oligocene elsewhere.
Average sedimentation rates range from 17 to 24 m/My in the Yumaque member of the Paracas Formation and increase to 147–170 m/My in the Otuma Formation. The microfossil assemblages witness a coastal setting with warm-temperate conditions for the Paracas Formation that become slightly cooler (though still temperate) in the upper Otuma Formation. Diatomaceous layers in the upper Otuma Formation indicate an overall increase in nutrient availability, which could reflect the global reorganization of ocean currents at the Eocene-Oligocene transition. However, the taxonomic composition of the diatom assemblage suggests seasonal rather than persistent upwelling conditions.
... The Protocetidae is a diverse paraphyletic family of archaic whales that constitute a major step in the evolutionary transition from land mammals to fully aquatic cetaceans (Gingerich et al., 2009;Bianucci and Gingerich, 2011). Protocetids were all quadrupedal swimmers but displayed diverse locomotor lifestyles from the amphibious basal forms to fully pelagic species (Buchholtz, 1998(Buchholtz, , 2007Hulbert, 1998;Luo and Gingerich, 1999;Gingerich, 2010;Gao and Ni, 2015;Bebej and Smith, 2017;Gingerich et al., 2019;Vautrin et al., 2020), and thanks to their inferred osmoregulatory capabilities (Clementz et al., 2006), were capable of crossing vast oceanic areas (Lambert et al., 2019). From their cradle in Pakistan, the group rapidly dispersed westward through the Tethys Seaway (Wang et al., 2002;Fordyce, 2018) to colonize most of the oceans of the planet in only a few million years from the early to the late Lutetian (Lambert et al., 2019). ...
... Protocetids were all quadrupedal swimmers but displayed diverse locomotor lifestyles from the amphibious basal forms to fully pelagic species (Buchholtz, 1998(Buchholtz, , 2007Hulbert, 1998;Luo and Gingerich, 1999;Gingerich, 2010;Gao and Ni, 2015;Bebej and Smith, 2017;Gingerich et al., 2019;Vautrin et al., 2020), and thanks to their inferred osmoregulatory capabilities (Clementz et al., 2006), were capable of crossing vast oceanic areas (Lambert et al., 2019). From their cradle in Pakistan, the group rapidly dispersed westward through the Tethys Seaway (Wang et al., 2002;Fordyce, 2018) to colonize most of the oceans of the planet in only a few million years from the early to the late Lutetian (Lambert et al., 2019). Although originating from Asia, the family name was coined based on early African discoveries (Stromer, 1908), following the description of Protocetus atavus from the middle Eocene Mokattam Formation in Egypt (Fraas, 1904). ...
... A matrix of 167 characters and 45 taxa has been assembled to assess the phylogenetic position of the new Togolese specimen. The core of this matrix is based on Geisler et al. (2005), and Gol'din and Zvonok (2013) supplemented with one additional character from Thewissen and Hussain (2000), one from Bianucci and Gingerich (2011), (20) from Mourlam and Orliac (2018), two from Gibson et al. (2019), two from Lambert et al. (2019) and (22) from Vautrin et al. (2020). Among them, 15 characters have been modified and/or split into new ones (see characters 2, 9, 10, 20, 30, 31, 45, 46, 53, 75, 87-92, 94, 116 and 124; see also Supplementary Text 1). ...
Earliest cetaceans (whales) originated from the early Eocene of Indo-Pakistan, but the group dispersed through most of the oceans of the planet by the late middle to late Eocene. This late Eocene global distribution indicates that important dispersal events took place during the middle Eocene (Lutetian), a globally undersampled time interval that is well documented in the Togolese phosphate series. We report here the first discovery of a partial cetacean cranium from middle Eocene deposits of Togo (West Africa). A 3D model of the cranium and teeth was reconstructed in order to reveal hidden anatomical features. The dental and cranial characteristics of the Togolese specimen recall those of protocetid taxa described in Africa, Asia, and North America, but also display significant differences. In particular, we show that the new specimen shares a number of morphological features with the Togolese taxon Togocetus. Such a hypothesis is further supported by a cladistic analysis including 45 taxa and 167 morphological characters, which recovers the new specimen close to Togocetus as the first offshoot of protocetids. Phylogenetic analysis including all the protocetids remains of Kpogamé confirms the singular diversity of the Togolese phosphate basin, and enables to examine potential connections with faunas from contemporaneous localities in Africa.
... The biogeographic distribution of stem cetaceans has been largely linked to their perceived locomotor capabilities. Pakicetids, ambulocetids, and remingtonocetids have been found only within the Tethys Ocean and have been perceived as more terrestrial, whereas the more aquatic protocetids are now known to have dispersed to the Americas (e.g., Hulbert et al. 1998;Uhen 1998;Geisler et al. 2005;Uhen 2014;Lambert et al. 2019a) and the fully aquatic basilosaurids are cosmopolitan (e.g., Köhler and Fordyce 1997;Uhen and Tichy 2000;Martínez-Cáceres and de Muizon 2011;Uhen et al. 2011;Uhen 2013Uhen , 2018. The tooth described here is provisionally identified as the first known remingtonocetid from the North America. ...
... A lack of previously discovered remingtonocetids from North America is unsurprising given that the record of protocetids is also sparse. Only 14 published fossil collections include protocetids from the Americas, with 13 from North America (Uhen 2014), one from South America (Lambert et al. 2019a), and several with very limited material. Indeed, only four of these North American collections are of Lutetian age, and all other known remingtonocetids from the Afro-Eurasia are Lutetian (Uhen 2020). ...
... Thus, lack of previous discoveries of remingtonocetids in North America is likely a problem of poor sampling. New discovery of protocetids from Peru (Lambert et al. 2019a) indicates that protocetids ranged much farther than previously thought, and perhaps, one should not be surprised by a North American remingtonocetid. ...
Remingtonocetid cetaceans are a group of stem whales known from the Indo-Pakistan and North African Tethys Ocean. An unusual tooth was discovered by Peter J. Harmatuk in 1973 in the middle Eocene Superior Stone Quarry (now the Martin Marietta Quarry) near Castle Hayne, North Carolina, USA. Here we identify this tooth as a premolar of a possible member of the Remingtonocetidae, which would extend the range of this family across the Atlantic to eastern North America. This partial tooth includes most of the crown (missing the mesial end) and the posterior root. The tooth bears a single central cusp and a worn accessory cusp on the posterior end. This tooth most closely resembles premolars of Remingtonocetus and is rather dissimilar to premolars of other archaeocetes known from the middle Eocene of North America, such as the families Protocetidae and Basilosauridae. This new record potentially expands the geographic distribution of the amphibious cetacean family Remingtonocetidae across the Atlantic.
... This transition involved major modifications to the generalized mammalian bodyplan to accommodate life in the seas, including modifications to the vertebral column and pelvis (Buchholtz, 2007;Uhen, 2014;Moran et al., 2015;Bebej and Smith, 2018), loss of hind limbs and emergence of flukepowered locomotion (Fish, 1998;Bejder and Hall, 2002;Uhen, 2004;Thewissen et al., 2006;Geisler, 2019), and emergence of a dorsopalmarly flattened forelimb embedded within a soft-tissue flipper (Richardson and Oelschläger, 2002;Uhen, 2004;Cooper et al., 2007bCooper et al., , 2018Sears et al., 2018). Specifically, this transition occurred during the Eocene, and whales from this period document these major skeletal changes related to the shift from a semi-terrestrial to a fully aquatic environment (Thewissen et al., 1996;Gingerich et al., 2001Gingerich et al., , 2009Madar, 2007;Houssaye et al., 2015;Lambert et al., 2019;Vautrin et al., 2019) (Fig. 1). Prior to the colonization of the sea, the earliest archaeocetes occupied shallow waters, probably returning to land for shelter and reproduction (Thewissen et al., 2009a). ...
... Protocetids are also described as semi-aquatic, and different taxa within the group are inferred to have employed different locomotor patterns (Gingerich, 2003;Lambert et al., 2019;Vautrin et al., 2019). There is a considerable amount of forelimb material described for this family, particularly for Maiacetus (Gingerich et al., 2009), Rodhocetus (Gingerich et al., 2001), Peregocetus (Lambert et al., 2019), and the newly published Senegalese protocetid (Vautrin et al., 2019). ...
... Protocetids are also described as semi-aquatic, and different taxa within the group are inferred to have employed different locomotor patterns (Gingerich, 2003;Lambert et al., 2019;Vautrin et al., 2019). There is a considerable amount of forelimb material described for this family, particularly for Maiacetus (Gingerich et al., 2009), Rodhocetus (Gingerich et al., 2001), Peregocetus (Lambert et al., 2019), and the newly published Senegalese protocetid (Vautrin et al., 2019). The carpi of these protocetids appear dorsopalmarly flattened as in modern cetaceans, and likely serve as a swimming adaptation. ...
During the land-to-water transition in the Eocene epoch, the cetacean skeleton underwent modifications to accommodate life in the seas. These changes are well-documented in the fossil record. The forelimb transformed from a weight-bearing limb with mobile joints to a flipper with an immobile carpus. We used micro-CT imaging to assess evolutionary changes in carpal size, orientation, and articulation within Eocene cetacean taxa associated with the transition from a terrestrial to amphibious niche. We compared Ambulocetus natans, a well-preserved amphibious archaeocete, with other archaeocetes, and with Eocene terrestrial artiodactyls, the sister group to Cetacea. A cylindrical carpus in terrestrial taxa evolved into a mediolaterally flattened, cambered carpus in the semi-aquatic and fully aquatic cetaceans. Specifically, the pisiform bone shifted from a ventral orientation in terrestrial taxa to a lateral orientation, in plane with the carpus, within semi-aquatic and fully aquatic taxa. Flattening of the carpus, including lateral rotation of the pisiform, likely relates to functional shifts from weight-bearing terrestrial locomotion to aquatic locomotion. This laterally projecting pisiform morphology is retained in all extant cetaceans. Our results suggest this shift, along with other modifications to the carpus, predominantly occurred during the middle Eocene and facilitated an obligatorily aquatic lifestyle in late Eocene cetaceans.
... le groupe souche des pélagicètes) sont au coeur de la transition entre un mode de vie amphibie et un mode de vie strictement aquatique (e.g. Marx et al. 2016 ;Lambert et al. 2019). D'ailleurs, dans sa définition première, la famille des protocétidés englobait l'ensemble des cétacés fossiles non pélagicètes, c'est-à-dire toutes baleines quadrupèdes semi-aquatiques (Stromer 1908 ;Kellogg 1936 ;Gingerich & Russell 1981, 1990voir aussi Hulbert et al. 1998). ...
... Cependant, il est possible de les définir de façon différentielle à partir des deux familles qui les encadrent dans l'arbre : les protocètes diffèrent des remingtonocètes par la présence d'un large processus supra-orbitaire (i.e. élargissement latéral des frontaux), des orbites plus larges, un crâne moins allongé, des vertèbres cervicales plus courtes, la présence d'une fovea capitis femoris [à l'exception des protocètes Natchitochia (Uhen 2014a) et Togocetus ] et un sacrum plus large avec moins de quatre vertèbres sacrées fusionnées Williams 1998 ;Bebej et al. 2015 ;Marx et al. 2016 ;Lambert et al. 2019). Par rapport aux basilosaures, les protocètes se distinguent en partie par la rétention de huit carpes (i.e. ...
... Par rapport aux basilosaures, les protocètes se distinguent en partie par la rétention de huit carpes (i.e. absence de fusion entre le capitatum et le trapézoïde), l'absence de denticules accessoires sur les dents jugales, la présence d'une M 3 (troisième molaire supérieure) et des molaires inférieures présentant un talonide Marx et al. 2016 ;Lambert et al. 2019). Bartonien (e.g. ...
La mise en évidence par la biologie moléculaire et par les données paléontologiques de l'appartenance des cétacés au groupe des artiodactyles constitue une des avancées majeures de ces 30 dernières années en mammalogie. Il n'y a cependant pas à l'heure actuelle de consensus quant aux relations phylogénétiques basales des artiodactyles fondées sur des caractères morphologiques et l'histoire évolutive du groupe est de fait, ponctuée de nombreux points d'interrogation. Cette thèse explore une source de caractères phylogénétiques prometteuse : la région auditive (os pétreux, bulle auditive, osselets de l'oreille moyenne, oreille interne) à partir notamment des nouvelles perspectives offertes par l'imagerie µCT Scan. Les principaux objectifs de cette thèse sont (1) de déterminer le signal phylogénétique porté par la région auditive chez les artiodactyles afin d’apporter une nouvelle source de caractères aux analyses et (2) d’explorer le signal écologique porté par les différents éléments de cette région sensorielle dédiée à l’audition (oreille externe, moyenne et canal cochléaire du labyrinthe osseux) et à l’équilibrioception (vestibule et canaux semi-circulaires du labyrinthe osseux). La première partie de cette thèse (I) nous emmène au Togo, où de nombreux restes inédits de la région auditive de « baleines à pattes » (Protocetidae Stromer, 1908) ont été récoltés. D’un point de vu anatomique, ces restes fossiles ont permis de documenter et de décrire pour la première fois le stapes, l’incus et le labyrinthe osseux d’un protocète ; des éléments indispensables pour comprendre leur audition. L’analyse morpho-fonctionnelle indique qu’une audition optimale était probablement possible dans l’air et dans l’eau pour ces cétacés semi-aquatiques. De plus, la morphologie de leur cochlée indique que leur capacité auditive était proche de celle de leurs cousins terrestres et que les spécialisations relatives aux capacités auditives remarquables des cétacés modernes (i.e. sensibilité aux infra- ou ultrasons) se sont opérées après la séparation historique entre les mysticètes et les odontocètes.La deuxième partie de ce travail (II) se concentre sur les origines de l’amphibiose au sein des Cetancodonta, à travers l’étude de plusieurs familles fossiles, connues pour leurs liens étroits au milieu aquatique. L’étude de la région auditive des hippopotamoïdes (Anthracotheriidae + Hippopotamidae), révèle que l’adaptation à un mode de vie semi-aquatique est apparue plusieurs fois, de façon convergente, dans son histoire évolutive et semble d’ailleurs indiquer une origine terrestre pour ce groupe. Quant au raoellidé Indohyus, son complexe pétro-tympanique présente une combinaison de caractères suggérant un certain degré d’adaptation au milieu aquatique, mais l’étude fonctionnelle de sa cochlée indique que ce taxon ne pouvait très probablement pas entendre de façon efficace sous l’eau. Pour finir, le dernier point de cette thèse explore également le potentiel phylogénétique de la région auditive à travers une analyse construite sur des caractères morphologiques du pétreux et du labyrinthe osseux à l’échelle des artiodactyles. Pour la première fois, les résultats de notre analyse concordent avec ceux des analyses moléculaires. Parmi les points les plus notables, le clade des Cetancodonta est bien soutenu par la morphologie du pétreux et la position d’Indohyus suggère fortement que les raoellidés sont des cétacés.Ainsi, la région auditive s’avère être un élément essentiel d’un point de vu phylogénétique et morphofonctionnel. En effet, comme nous avons pu le voir tout au long de cette thèse, lorsque la nature complexe et variée de la région auditive est appréhendée dans son ensemble, elle permet d’inférer l’écologie d’un taxon donné et d’en apprendre davantage sur ses relations de parenté. Par conséquent, la région auditive est encore loin d’avoir dit ses derniers mots... et nous n’avons pas encore fini d’en entendre parler.
... Genera included in each subfamily of Protocetidae are listed in a table below (see Discussion). The classification here is generally consistent with most recent phylogenetic analyses of Eocene cetaceans [2,[6][7]. ...
... Forelimbs and hind limbs of Aegicetus gehennae differ in detail from forelimbs and hind limbs of protocetines described to date [4][5]7], but the most important functional difference in Aegicetus appears to be the large size of the manus compared to the pes, or, stating this another way, the small size of the pes compared to the manus (Fig 22). The ratio of Mc-III metacarpal length to Mt-III metatarsal length is 0.94 in A. gehennae, and comparable ratios are 0.64, 0.73, and 0.76 for Rodhocetus balochistanensis [4][5], Maiacetus inuus [5], and Peregocetus pacificus [7]. ...
... Forelimbs and hind limbs of Aegicetus gehennae differ in detail from forelimbs and hind limbs of protocetines described to date [4][5]7], but the most important functional difference in Aegicetus appears to be the large size of the manus compared to the pes, or, stating this another way, the small size of the pes compared to the manus (Fig 22). The ratio of Mc-III metacarpal length to Mt-III metatarsal length is 0.94 in A. gehennae, and comparable ratios are 0.64, 0.73, and 0.76 for Rodhocetus balochistanensis [4][5], Maiacetus inuus [5], and Peregocetus pacificus [7]. Ratios of Mc-III and Mt-III diameters would tell a similar story. ...
Aegicetus gehennae is a new African protocetid whale based on a partial skull with much of an associated postcranial skeleton. The type specimen, Egyptian Geological Museum, Cairo [CGM] 60584, was found near the base of the early-Priabonian-age (earliest late Eocene) Gehannam Formation of the Wadi Al Hitan World Heritage Site in Egypt. The cranium is distinctive in having ventrally-deflected exoccipitals. The vertebral column is complete from cervical C1 through caudal Ca9, with a vertebral formula of 7:15:4:4:9+, representing, respectively, the number of cervical, thoracic, lumbar, sacral, and caudal vertebrae. CGM 60584 has two more rib-bearing thoracic vertebrae than other known protocetids, and two fewer lumbars. Sacral centra are unfused, and there is no defined auricular surface on the ilium. Thus there was no weight-bearing sacroiliac joint. The sternum is distinctive in being exceptionally broad and flat. The body weight of CGM 60584, a putative male, is estimated to have been about 890 kg in life. Long bones of the fore and hind limbs are shorter than expected for a protocetid of this size. Bones of the manus are similar in length and more robust compared to those of the pes. A log vertebral length profile for CGM 60584 parallels that of middle Eocene Maiacetus inuus through the anterior and middle thorax, but more posterior vertebrae are proportionally longer. Vertebral elongation, loss of a sacroiliac articulation, and hind limb reduction indicate that Aegicetus gehennae was more fully aquatic and less specialized as a foot-powered swimmer than earlier protocetids. It is doubtful that A. gehennae had a tail fluke, and the caudal flattening known for basilosaurids is shorter relative to vertebral column length than flattening associated with a fluke in any modern whale. Late protocetids and basilosaurids had relatively long skeletons, longer than those known earlier and later, and the middle-to-late Eocene transition from foot-powered to tail-powered swimming seemingly involved some form of mid-body-and-tail undulation.
... However, the presence of Peregocetus in Peru more compatible with an openwater crossing of the South Atlantic. Lambert and colleagues [7] further expand upon this scenario by suggesting that early whales dispersed to South America first, then turned south along its Pacific coast, and finally dispersed to North America. While this is the most parsimonious hypothesis given the known fossils and their ages, the unexpected location and age of Peregocetus give some credence to an earlier suggestion of dispersal via the Pacific Ocean, instead of the Atlantic Ocean [9]. ...
... The tail of Peregocetus suggests another possibility. Lambert and colleagues [7] note that its caudal vertebrae have more robust Reconstruction of the archaic whale Maiacetus innus, a close relative of Peregocetus pacificus, described in this issue of Current Biology [7]. If subaqueous cephalic parturition was common, as shown here and seen in the hippopotamus, then it is unclear why whales of this evolutionary grade would have left the water, despite having large hindlimbs (artwork: ª Carl Buell). ...
... The tail of Peregocetus suggests another possibility. Lambert and colleagues [7] note that its caudal vertebrae have more robust Reconstruction of the archaic whale Maiacetus innus, a close relative of Peregocetus pacificus, described in this issue of Current Biology [7]. If subaqueous cephalic parturition was common, as shown here and seen in the hippopotamus, then it is unclear why whales of this evolutionary grade would have left the water, despite having large hindlimbs (artwork: ª Carl Buell). ...
A 43 million-year-old fossil whale from Peru marks the first record of whales in the Western Hemisphere. Its large feet were used for swimming, but a wide tail may have enabled whales to expand beyond the Tethys Sea.
... The earliest trans-Atlantic dispersal of cetaceans probably occurred between~45.7 and 43.3 Ma (Gohar et al., 2021) and gave rise to the archaeocetes Peregocetus from Peru (Lambert et al., 2019) and Carolinacetus from North America (Geisler, Sanders & Luo, 2009). This temporal window does not overlap with our estimate for the dispersal of prorastomids from the Tethys to the Caribbean. ...
... We further note that it is not the case that there are no Paleogene marine deposits in which eastern Pacific sirenians could be preserved. For instance, the highly productive middle-to-late Eocene deposits of the Pisco Basin in Peru have not yet yielded remains of sirenians, whereas cetaceans and other marine megafauna are well-documented (Lambert et al., 2019;Malinverno et al., 2021). Similarly, the late Oligocene El Cien and San Gregorio formations of Baja California Sur have produced abundant cetaceans and elasmobranchs (among other marine vertebrates), but sea cows are absent from these assemblages thus far (Hernández Cisneros, González Barba & Fordyce, 2017). ...
Molecular phylogenetic studies that have included sirenians from the genera Trichechus, Dugong, and Hydrodamalis have resolved their interrelationships but have yielded divergence age estimates that are problematically discordant. The ages of these lineage splits have profound implications for how to interpret the sirenian fossil record — including clade membership, biogeographic patterns, and correlations with Earth history events. In an effort to address these issues, here we present a total evidence phylogenetic analysis of Sirenia that includes living and fossil species and applies Bayesian tip-dating methods to estimate their interrelationships and divergence times. In addition to extant sirenians, our dataset includes 56 fossil species from 106 dated localities and numerous afrotherian outgroup taxa. Genetic, morphological, temporal, and biogeographic data are assessed simultaneously to bring all available evidence to bear on sirenian phylogeny. The resulting time-tree is then used for Bayesian geocoordinates reconstruction analysis, which models ancestral geographic areas at splits throughout the phylogeny, thereby allowing us to infer the direction and timing of dispersals. Our results suggest that Pan-Sirenia arose in North Africa during the latest Paleocene and that the Eocene evolution of stem sirenians was primarily situated in the Tethyan realm. In the late Eocene, some lineages moved into more northern European latitudes, an area that became the source region for a key trans-Atlantic dispersal towards the Caribbean and northern-adjacent west Atlantic. This event led to the phylogenetic and biogeographic founding of crown Sirenia with the Dugongidae-Trichechidae split occurring at the Eocene-Oligocene boundary (~33.9 Ma), temporally coincident with the onset of dropping global sea levels and temperatures. This region became the nexus of sirenian diversification and supported taxonomically-rich dugongid communities until the earliest Pliocene. The Dugonginae-Hydrodamalinae split occurred near Florida during the early Miocene (~21.2 Ma) and was followed by a west-bound dispersal that gave rise to the Pacific hydrodamalines. The late middle Miocene (~12.2 Ma) split of Dugong from all other dugongines also occurred near Florida and our analyses suggest that the Indo-Pacific distribution of modern dugongs is the result of a trans-Pacific dispersal. From at least the early Miocene, trichechid evolution was based entirely in South America, presumably within the Pebas Wetlands System. We infer that the eventual establishment of Amazon drainage into the South Atlantic allowed the dispersal of Trichechus out of South America no earlier than the mid-Pliocene. Our analyses provide a new temporal and biogeographic framework for understanding major events in sirenian evolution and their possible relationships to oceanographic and climatic changes. These hypotheses can be further tested with the recovery and integration of new fossil evidence.
PeerJ 10:e13886 http://dx.doi.org/10.7717/peerj.13886
... The tail flukes of cetaceans act as a single propulsor and control surface. [10][11][12] Although biologists have a thorough understanding of the anatomy of the flukes, 13-20 the biomechanical consequences, 11,12,18,19,21 and the evolutionary history of tail flukes, [22][23][24][25] no data yet add insights into molecular mechanisms created the flukes. ...
Background
During the land‐to‐sea transition of cetaceans (whales, dolphins, and porpoises), the hindlimbs were lost and replaced by an elaborate tail fluke that evolved 32 Ma. All modern cetaceans utilize flukes for lift‐based propulsion, and nothing is known of this organ's molecular origins during embryonic development. This study utilizes immunohistochemistry to identify the spatiotemporal location of protein signals known to drive appendage outgrowth in other vertebrates (e.g., Sonic Hedgehog [SHH], GREMLIN [GREM], wingless‐type family member 7a [WNT], and fibroblast growth factors [FGFs]) and to test the hypothesis that signals associated with outgrowth and patterning of the tail fluke are similar to a tetrapod limb. Specifically, this study utilizes an embryo of a beluga whale ( Delphinapterus leucas ) as a case study.
Results
Results showed epidermal signals of WNT and FGFs, and mesenchymal/epidermal signals of SHH and GREM. These patterns are most consistent with vertebrate limb development. Overall, these data are most consistent with the hypothesis that outgrowth of tail flukes in cetaceans employs a signaling pattern that suggests genes essential for limb outgrowth and patterning shape this evolutionarily novel appendage.
Conclusions
While these data add insights into the molecular signals potentially driving the evolution and development of tail flukes in cetaceans, further exploration of the molecular drivers of fluke development is required.
... The East Pisco Basin is comprised of a larger onshore portion and a smaller submerged part; it is separated from the more seaward West Pisco Basin by an NW-trending alignment of basement elevations known as the Outer Shelf High (Thornburg and Kulm, 1981;Di Celma et al., 2022). The onshore part of the East Pisco Basin is home to one of the most renowned Cenozoic marine Fossil-Lagerstätte whose fossil content includes both vertebrates (e.g., Clarke et al., 2010;Lambert et al., 2010Lambert et al., , 2017Lambert et al., , 2019Esperante et al., 2015;Gioncada et al., 2016;Marx et al., 2017;Bianucci et al., 2018bBianucci et al., , 2023Collareta et al., 2021;Bosio et al., 2021b;Bianucci and Collareta, 2022) and invertebrates (e.g., DeVries, 1988DeVries, , 2007DeVries, , 2016DeVries and Frassinetti, 2003;Coletti et al., 2019;Collareta et al., 2019Collareta et al., , 2023Bosio et al., 2021a;Kočí et al., 2021;Sanfilippo et al., 2021). ...
... The protocetid whale, Maiacetus ( Fig. 4.1c), is known from two skeletons that are about 12% different in size, leading to the conclusion of sexual dimorphism in total body size, with the males being larger than females (Gingerich et al. 2009). Peregocetus, a quadrupedal protocetid found in Peru from sediments dating to the middle Eocene, showed the sacrum was attached to the pelvis, the hindlimb was functional in both terrestrial and aquatic locomotion, and the digits were capped with small hooves (Lambert et al. 2019). Morphology of the vertebral column suggested aquatic locomotion was supported by a powerful tail that likely functioned in concert with the hindlimbs during aquatic locomotion, similar to modern otters (Geisler 2019). ...
The earliest fossil cetaceans (archaeocetes) dramatically shifted the shape and articulation of the pelvis and hindlimbs during the land-to-sea transition. Archaeocetes were mostly semi-aquatic “walking whales” that used powerful hindlimbs to walk on land and swim to reach new aquatic sources of food. However, skeletons of the latest diverging lineages of archaeocetes, the basilosaurids, showed that the pelvis initially lost articulation with the sacrum, and hindlimbs were reduced and encased within the body wall. Consequently, basilosaurids were no longer able to bear their weight on land and probably had a different mating strategy compared to the other archaeocetes. Basilosaurid mating behaviors were probably consistent with those of modern cetaceans, including lateral- and ventral-facing copulation. Moreover, a pelvic girdle that was no longer constrained by vertebral and limb attachments likely freed fetal development from size constraints at birth, allowing for the birth of large fetuses. This study reports new data showing growth of the pelvis with age in modern bowhead whales ( Balaena mysticetus ) and their implications for left-right asymmetry and sex difference in pelvic dimensions among modern cetaceans. Reproductive structures present in modern cetaceans and artiodactyls were probably present in archaeocetes, including pelvic attachment of muscles associated with erection and mobility of the penis, the ischiocavernosus, in males and the clitoris of females. Within females, transverse folds along the vaginal canal are present in some terrestrial artiodactyls, modern cetaceans, and probably archaeocetes. Vaginal folds were probably exapted to assist in successful aquatic copulation in all fossil and modern cetaceans as they may protect some sperm from the lethal effects of sea water. Taken together, shifts in the pelvic girdle of cetaceans occurred over 40 million years ago and probably required changes in mating behaviors that were consistent with those seen in modern cetaceans.
... First, research on Oligocene mysticetes has largely focused on toothed mysticetes and eomysticetids, so it is possible that more effort in searching for early possible crown mysticetes will lead to relevant fossils being found outside New Zealand (e.g. the phylogenetic position of Tlaxcallicetus requires further research). Toipahautea, Whakakai, Horopeta, Mauicetus, and other undescribed specimens discovered to date represent abundant and relatively large mysticetes from the Oligocene deposits of New Zealand (Figure 3), and long-distance migration or dispersal is common in cetaceans (from Eocene archaeocetes [Lambert et al. 2019] to Pleistocene mysticetes [Tsai and Chang 2019]). Therefore, large species such as these are unlikely to have only inhabited New Zealand during the Oligocene but more likely experienced global radiation, a topic that requires further attention and research effort worldwide. ...
Recent research on mysticete fossils from the Late Eocene and Oligocene has revolutionised our understanding of the diversity and evolutionary scenarios for early baleen whales. For example, aetiocetids are a possible, though controversial, lineage that bridges the gap between the toothed and baleen-bearing mysticetes, and eomysticetids show a further transitional step towards the baleen-bearing status, with the presence of nonfunctional dentition in adults. However, information about the origin of crown mysticetes, including the most recent common ancestor of all extant lineages and its descendants, is critical to further understanding the evolution of baleen whales. The phylogenetic positions of the Oligocene Toipahautea, Whakakai, Horopeta, and Mauicetus from New Zealand remain unresolved and problematic, but all four genera show a close relationship with crown mysticetes. The original and subsequent cladistic analyses have consistently revealed a sister relationship between the Toipahautea-to-Mauicetus grade and crown mysticetes, and Horopeta has been placed close to the cetotheriids within the crown group. This review aims to stimulate more research on this topic by elucidating the origin of crown mysticetes, which likely experienced a poorly known radiation event during the Oligocene that established the modern lineages.
... edu/ wp/ proto cetid ae/). The pentagonal shape of the distal epiphyseal side (lacking the epiphysis) in NMRx1799 well resembles the distal epiphysis of the tibiae of A. gehennae and Peregocetus pacificus Lambert et al., 2019 (as seen on photos provided by O. Lambert). The LWR of 0.94 in NMRx1799 is slightly less than that of the protocetids A. gehennae (Fig. 7i; Table 8) and P. pacificus (Appendix Table 12): both 1.04 (the latter estimated from photos given by O. Lambert). ...
Transition of cetaceans from a semi-aquatic to a fully aquatic lifestyle during the Eocene involved numerous transformations of their anatomy, including reduction of the hind limbs. The earliest fully aquatic cetaceans retained externally protruding, possibly functional hind limbs. Being extremely rare, every find of archaeocete hind limb elements can improve our knowledge on the evolution of locomotor strategies in cetaceans. Here, we describe the anatomy and inner microstructure of an isolated tibia fragment, that has been found in the Middle Eocene of Helmstedt, present-day Germany, with comments on its affinities and function. Assignment to an archaeocete is most probable, as other, presently known taxa could be excluded, because of the shape of the distal epiphyseal side and the internal architecture. Nevertheless, it cannot be ruled out with complete certainty that this isolated tibia belongs to a taxon that is new, or is at this moment unknown from coeval sediments of Europe. Well-developed, distally extended tibial crests could indicate the capability of movements with the foot and thus feet-induced aquatic locomotion. The tibia fragment may belong to a large member of semi-aquatic cetaceans (Protocetidae) or to a member of Basilosauridae, early fully aquatic whales. It shares gross and inner morphological features with tibiae of Protocetidae. In this case, it could be from a large protocetid, certainly more than 4 m long, and would be the first protocetid find in Europe as well as the northernmost record of this family in the world. Alternatively, the tibia may belong to a representative of Basilosauridae, which have been found in different parts of Europe, including the region of Helmstedt. If so, it would imply that early basilosaurids had large, protocetid-like hind limbs. This record shows that large quadrupedal cetaceans inhabited the seas of Northwestern Europe by the late Middle Eocene. Not-related finds of our studies are that the terrestrial lifestyle of the artiodactyl Anoplotherium is confirmed by the inner structure of its long bones, and that some species of the perissodactyl Lophiodon were most probably semi-aquatic, as shown by the inner microstructure of the tibia.
... The Eocene to Pliocene(?) sedimentary fill of the East Pisco Basin, southern coast of Peru, hosts one of the greatest concentrations worldwide of Cenozoic marine vertebrate fossils (e.g., Clarke et al. 2007;Clarke et al. 2010;Lambert et al. 2010;Lambert et al. 2017b;Lambert et al. 2019;. Whereas the oldest portion of the basin fill is still somewhat understudied, the primarily Miocene Chilcatay and Pisco formations are now reasonably well known, both geologically and palaeontologically, based on extensive researching in the past four decades (Muizon & DeVries 1985;Bianucci et al. 2010;Bianucci et al. 2016a;Bianucci et al. 2016b;Bianucci et al. 2019;Collareta et al. 2015;Collareta et al. 2017b;Collareta et al. 2020;Collareta et al. 2021a;Collareta et al. 2021b;Collareta et al. 2022;Collareta et al. 2023a;Collareta et al. 2023b;Stucchi et al. 2015;Di Celma et al. 2016a;Di Celma et al. 2016b;Di Celma et al. 2017;Di Celma et al. 2018a;Di Celma et al. 2018b;Di Celma et al. 2019;Di Celma et al. 2022;Gioncada et al. 2016;Di Celma et al. 2018a;Di Celma et al. 2018b;Lambert et al. 2009;Lambert et al. 2010;Lambert et al. 2015a;Lambert et al. 2015b;Lambert et al. 2017a;Lambert et al. 2018;Lambert et al. 2020;Lambert et al. 2021;Landini et al. 2017a;Landini et al. 2017b;Landini et al. 2019;Marx et al. 2017;Bosio et al. 2020a;Bosio et al. 2020b;Bosio eschweizerbart_xxx et al. 2021a;Bosio et al. 2021b;Bosio et al. 2022;Benites-Palomino et al. 2022). ...
An upper anterior tooth of Cosmopolitodus hastalis (Elasmobranchii: Lamnidae) from Burdigalian strata of the shallow-marine Chilcatay Formation exposed at Zamaca (East Pisco Basin, Peru) exhibits the remarkable occurrence of a serrated bite mark consistent with Linichnus serratus (Praedichnia: Machichnidae). In marine successions of Cenozoic age, traces belonging to the ich-nogenus Linichnus are typically found occurring on the bones of marine mammals and interpreted as due to predation or scavenging by sharks provided with smooth-edged (Linichnus bromleyi) or denticulated (L. serratus) teeth. Only a few fossil shark teeth exist preserving serrated bite marks, all of which have been interpreted as due to self-biting, which may occur when a shark loses a tooth while feeding and accidentally bites into it. Since C. hastalis is a smooth-toothed species, self-biting cannot explain our unusual find of L. serratus, which in turn may either reflect some kind of trophic interaction between large carnivorous sharks (with a late juvenile or young adult C. hastalis being fed upon by another elasmobranch, possibly a large-sized carcharhinid) or testify to accidental biting during multispecies shark scavenging on the carcass of a third organism that did not get preserved alongside the bitten tooth.
... Revista Minerva • ISSN 2521-8794 • Edición Especial Mamíferos Marinos • San Salvador, El Salvador, C.A. • 5(1) • pp. 92-101 Reconstruyendo los cetáceos fósiles: Una perspectiva moderna El siguiente taxón representa una etapa intermedia de los cetáceos, siendo Protocetus atavus, un cetáceo del Lutetiano (entre 48.6 a 40.4 millones de años), perteneciente a la familia Protocetidae(Fornasiero y Del Favero, 2014), el cual a menudo era y es en ocasiones, representado como una ballena adaptada al agua, con cola y aleta pero con la peculiaridad de tener las 4 extremidades visibles (Figura 6); no obstante, ahora se sabe que los miembros de la familia Protocetidae poseían extremidades fuertes y les permitían caminar en tierra pero también nadar(Lambert et al. 2019). Tomando en cuenta las revisiones y a pesar de no poseer el esqueleto completo de Protocetus, Nueva ilustración de Protocetus atavus, ilustración Jaime Bran. ...
La ilustración científica ha sido una herramienta de gran importancia en la presentación y divulgación de la ciencia, en la paleontología lo es aún más porque permite visualizar cómo eran los organismos extintos por medio de inferencias e hipótesis basadas en la ciencia, comúnmente denominada paleoarte. Este artículo trata de la reconstrucción paleoartística de algunos representantes clave en la historia evolutiva de los cetáceos: Pakicetus attocki, Protocetus atavus, Zygorhiza kochii, Basilosaurus isis y Mystacodon selenensis contrastaron con representaciones antiguas de estos animales para reflejar los cambios que han traído las publicaciones científicas recientes en cuanto a su anatomía y otros aspectos ecológicos que nos ayudan a comprender mejor a estos animales.
... Early amphibious fossil whales are hypothesized to have partial interdigital webbing on the limbs (Gingerich et al., 2001(Gingerich et al., , 2009(Gingerich et al., , 2019Lambert et al., 2019;Madar, 2007;Thewissen et al., 1996) By the emergence of Dorudon, the first pelagic archaeocete, the forelimb was completely encased in a soft-tissue flipper (Uhen, 2004), though there is no evidence of hyperphalangy. Some of the earliest evidence for hyperphalangy is in the 7-8 MYA mysticete fossil Balaenoptera siberi (Pilleri, 1990) (Amasaki et al., 1989;Sedmera et al., 1997a). ...
Embryogenesis of cetaceans (whales, dolphins, porpoises) is well known in Stenella attenuata, the pan-tropical spotted dolphin, based on a remarkably complete and well-studied series prenatal ontogenetic stages. Our study expands understanding of cetacean embryology by adding two additional cetacean taxa: the beluga whale (Delphinapterus leucas, Odontoceti), and the bowhead whale (Balaena mysticetus, Mysticeti). We identify key features that characterize these taxa at specific stages and highlight heterochrony between the odontocetes and mysticetes. A presomitic Delphinapterus embryo is also described. This study therefore applies the Carnegie staging system to two more cetacean taxa and forms a framework for future research on cetacean developmental genetics and modeling of fetal growth.
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... Sedimentation rates were also correlated with the dolomite stoichiometry, with low (46-52%) or high (52-58%) % mol CaCO3 under high and low sediment accumulation rates, respectively in the basins off Peru (Kulm et al., 1984). In the dolomite layers of the P2 sequence analysed Table 1 Sedimentation rates of important recent and past upwelling settings (Friedman and Murata, 1979;Lambert et al., 2017Lambert et al., , 2019Malinverno et al., 2021;Marty, 1989;Schrader, 1982;Skilbeck and Fink, 2006;Suess and Von Huene, 1988;Wefer et al., 1998 here, molar % CaCO 3 ranges from 49.5 to 58% and is rather consistent within each layer, but no significant correlation was found between the sediment nature (biogenic vs. terrigenous) and CaCO 3 % in dolomite, suggesting a more complex control. The two dolomite layers analysed for δ 13 C provide some insight, although our sample selection might have biased our potential of interpreting the diagenetic environment. ...
Along the Peruvian coast, the sedimentary succession of the East Pisco Basin is exposed in the Ica Desert. At Cerro Los Quesos, laterally continuous dolomite layers characterise the diatomaceous sediments of the P2 sequence of the Miocene Pisco Formation, where a large number of marine vertebrates are exceptionally preserved, many enclosed in dolomite nodules. In this work, cemented layers from this sequence were described and sampled for petrographic, chemical, microscopic and isotopic analyses. Dolomite occurs in continuous 10–50 cm thick well cemented layers, formed by sediment of different nature: biogenic, terrigenous, volcanoclastic, and phosphatic. The underlying sediments exhibit a yellow layer with sparse dolomite crystals, a black layer with abundant Mn-oxides, and a reddish layer rich in Fe-oxides, indicating redox-related fronts. Two generations of dolomite can be recognised: an early diagenetic microcrystalline one, and a sparry one, filling the large cavities. As observed in both thin sections and on broken surfaces, microcrystalline dolomite also fills the inner spaces of the diatom areolae replicating their finest ultrastructure, such as foramina and cribra and replace calcite shells of foraminifera. δ¹⁸O and δ¹³C values from the microcrystalline dolomite of two layers, selected based on the absence of other carbonate phases (e.g. calcite) and the lack of sparry cement, are in agreement with those reported for the Peru margin and fall in the fields of either sulphate-reduction or methanogenesis.
All the data point to dolomite precipitation associated with low-temperature early diagenesis that typically occurs in upwelling settings, where high surface water productivity is responsible for high rates of organic carbon flux to the sea bottom and for the cyclical oxygen depletion at the bottom. Such conditions also promote high abundances of marine vertebrates and the exceptional preservation of their skeletons in the sediments.
... The rich fossil record from the southeastern Pacific (SEP) in the coastal desert of Peru has revealed invaluable data about the evolution of marine vertebrates and their ecosystems for the last 42 million years (e.g. [25][26][27]). Along with whales, earless seals, penguins and aquatic sloths, most of the Neogene localities of the Pisco Formation have yielded well-preserved remains of crocodylians [26,27], until now represented by one giant gavialid species, Piscogavialis jugaliperforatus Kraus, 1998 [13]. ...
The evolution of crocodylians as sea dwellers remains obscure because living representatives are basically freshwater inhabitants and fossil evidence lacks crucial aspects about crocodylian occupation of marine ecosystems. New fossils from marine deposits of Peru reveal that croco-dylians were habitual coastal residents of the southeastern Pacific (SEP) for approximately 14 million years within the Miocene (ca 19 to 5 Ma), an epoch including the highest global peak of marine crocodylian diversity. The assemblage of the SEP comprised two long and slender-snouted (long-irostrine) taxa of the Gavialidae: the giant Piscogavialis and a new early diverging species, Sacacosuchus cordovai. Although living gavialids (Gavialis and Tomistoma) are freshwater forms, this remarkable fossil record and a suite of evolutionary morphological analyses reveal that the whole evolution of marine crocodylians pertained to the gavialids and their stem relatives (Gavialoidea). This adaptive radiation produced two longirostrine eco-morphs with dissimilar trophic roles in seawaters and involved multiple transmarine dispersals to South America and most landmasses. Marine gavialoids were shallow sea dwellers, and their Cenozoic diversification was influenced by the availability of coastal habitats. Soon after the richness peak of the Miocene, gavialoid crocodylians disappeared from the sea, probably as part of the marine megafauna extinction of the Pliocene.
... Por otro lado, el aplanamiento dorsoventral de las falanges está vinculado al desarrollo de membranas interdigitales en manos y pies, característica importante en la propulsión natatoria (2). Finalmente, las vértebras caudales presentan procesos trasversos expandidos y bifurcados (al igual que en otros mamíferos semiacuáticos), los cuales implican la presencia de una cola poderosa que proporciona un mayor empuje durante el nado (2,6). ...
La nutria marina, Lontra felina, es un carnívoro generalista con marcadas diferencias en la dieta a lo largo de su distribución en las costas del Pacífico sudeste, pues las poblaciones del norte (Perú) son principalmente piscívoras, mientras que las del sur (Chile) son predominantemente durófagas (e.g. crustáceos). Diferencias alimenticias existen entre especies vivientes de nutrias (Lutrinae) y han sido asociadas a disparidad en las proporciones del cráneo y la mandíbula. Dado que L. felina no ha sido incluida en análisis cuantitativos, se desconoce si su anatomía corresponde con alguno de los ecomorfotipos establecidos para las nutrias –piscívoro o durófago– y si éste presenta variaciones geográficas o sexuales. El objetivo de este estudio fue establecer el ecomorfotipo de alimentación de Lontra felina en un contexto filogenético e investigar su variación morfológica intraespecífica. Utilizando morfometría geométrica, se cuantificó la morfología craneal y mandibular de especímenes de Lontra felina de Perú y Chile y otras 15 especies de mustélidos. La comparación interespecífica se realizó mediante análisis de componentes principales con mapeo filogenético y las variaciones intraespecíficas se evaluaron usando análisis discriminantes y pruebas de t. Los análisis morfométricos demostraron que la nutria marina presenta un ecomorfotipo alimenticio mixto, con características tanto del piscívoro (cráneos más alargados, planos y estrechos, mandíbulas más alargadas y procesos angulares más grandes) como del durófago (cráneos más cortos, convexos y anchos, áreas molariformes más grandes y mandíbulas más cortas). Los análisis intraespecíficos indicaron la ausencia de dimorfismo sexual, pero revelaron diferencias geográficas en la forma asociadas a la variación latitudinal en la dieta entre Perú y Chile. Así, las poblaciones de Perú exhibieron cráneos más alargados y estrechos, propios del ecomorfotipo piscívoro, y, las de Chile, cráneos más cortos y anchos, típicos del ecomorfotipo durófago. Considerando las diferencias genéticas previamente reportadas, nuestros resultados apoyan la existencia de un proceso de especiación alopátrica en marcha conducido por la dieta y cuyo conocimiento es de relevancia para su conservación.
... The Miocene and early Pliocene fossil record of marine mammals from the southwestern coast of South America is taxonomically and ecologically diverse and comprises an exceptional number of taxa, including cetaceans, pinnipeds, sirenians and aquatic sloths (Muizon 1981;Muizon & Domning 1985;Gutstein et al. 2009Gutstein et al. , 2015Lambert et al. 2010;Valenzuela-Toro et al. 2013;Amson and Muizon, 2014;Pyenson et al. 2014;De Los Arcos et al. 2017;Tanaka et al. 2017;Benites-Palomino et al. 2020a). The fossils from this region have provided critical evidence concerning some of the principal milestones in the evolution of marine faunae (e.g., Lambert et al. 2017Lambert et al. , 2019. Contrasting with this relative rich record, the fossil record of marine mammals from Pleistocene localities is still poorly known and fragmentary, being constituted by few isolated or fragmentary remains of pinnipeds from Chile (Valenzuela-Toro et al. 2013; and cetaceans and pinnipeds from Peru (DeVries 1986). ...
The fossil record of marine mammals from the upper Pliocene of the western coast of South America is poorly known, hindering our knowledge about how and when marine mammal faunas attained their modern distribution in the area. Here, we describe a new marine mammal assemblage from the Horcón Formation (upper Pliocene), located in the Valparaíso Region of central Chile. The material reported comprises postcranial remains of an indeterminate seal (Phocidae), Delphinoidea vertebrae, and mysticete elements (still in the field). The Phocidae remains constitute the youngest pre-Pleistocene record of this family in South America, providing new information regarding the timing for the establishment of the modern diversity and distribution of pinnipeds in the Southern Hemisphere. Furthermore, the pinniped and cetacean remains reported indicate that the marine mammal assemblage from the upper Pliocene along central Chile was composed of a mixture of modern and extinct taxa.
... Protocetids, which comprise a paraphyletic grade, were probably the earliest trans-oceanic cetaceans but also spent time on land, where they may have given birth and nursed their young. 105,113,114 These forms would certainly have looked different than modern whales due to their more prominent hindlimbs and primitive cranial morphology, but in other respects, such as having a largely hairless body, may have been similar to modern cetaceans. ...
The macroevolutionary transition from terra firma to obligatory inhabitance of the marine hydrosphere has occurred twice in the history of Mammalia: Cetacea and Sirenia. In the case of Cetacea (whales, dolphins, and porpoises), molecular phylogenies provide unambiguous evidence that fully aquatic cetaceans and semiaquatic hippopotamids (hippos) are each other’s closest living relatives. Ancestral reconstructions suggest that some adaptations to the aquatic realm evolved in the common ancestor of Cetancodonta (Cetacea + Hippopotamidae). An alternative hypothesis is that these adaptations evolved independently in cetaceans and hippos. Here, we focus on the integumentary system and evaluate these hypotheses by integrating new histological data for cetaceans and hippos, the first genome-scale data for pygmy hippopotamus, and comprehensive genomic screens and molecular evolutionary analyses for protein-coding genes that have been inactivated in hippos and cetaceans. We identified eight skin-related genes that are inactivated in both cetaceans and hippos, including genes that are related to sebaceous glands, hair follicles, and epidermal differentiation. However, none of these genes exhibit inactivating mutations that are shared by cetaceans and hippos. Mean dates for the inactivation of skin genes in these two clades serve as proxies for phenotypic changes and suggest that hair reduction/loss, the loss of sebaceous glands, and changes to the keratinization program occurred ∼16 Ma earlier in cetaceans (∼46.5 Ma) than in hippos (∼30.5 Ma). These results, together with histological differences in the integument and prior analyses of oxygen isotopes from stem hippopotamids (“anthracotheres”), support the hypothesis that aquatic skin adaptations evolved independently in hippos and cetaceans.
... Undoubtedly, GMTSNUK 2638 is a representative of fully aquatic cetaceans, Pelagiceti. It presents several characters shared by Basilosauridae and Neoceti (Uhen, 2008): a broad, fan-shaped scapula like in all the fully aquatic cetaceans (Uhen, 2004;Lambert et al., 2017) and different from a narrow scapula of protocetids (e.g., Peregocetus or Maiacetus) (Gingerich et al., 2009;Lambert et al., 2019), as well as no signs of attachment for pelvics on the vertebrae from the sacral region. Also, the anteroposteriorly elongated vertebral centra, neural arches and transverse processes of vertebrae (once considered as diagnostic for Platyosphys) are shared by a few earliest Pelagiceti: Basilotritus spp. ...
The earliest fully aquatic cetaceans arose during the Middle Eocene; however, the earliest stage of their divergence is obscure. Here, we provide a detailed redescription of an unusual early cetacean, “Platyosphys einori”, from the Late Eocene of Ukraine (37.8–35.8 million years ago), with new data on its body size, skeletal microanatomy and suggestions on phylogenetic relationships. The procedure of regression analysis has been developed for the body size estimation from the size of the longest vertebra and the width of a cervical vertebra. “Platyosphys einori”, identified here as Basilosauridae incertae sedis, is a fully aquatic cetacean with a pronounced neck, poorly developed or low frequency underwater hearing, and it has a mix of plesiomorphic and derived traits. It is unusually large for a cetacean of that time, approximately 10 m long, and it is possibly very young and fast-growing for its body size. There is no pachyosteosclerotic cortex in vertebrae, and there is a large amount of spongy tissue in the rib. Therefore, “Platyosphys einori”, even if juvenile, is at the intermediate stage between early cetaceans with osteosclerotic bones and modern whales with osteoporotic skeleton. Thus, “Platyosphys einori” shows adaptations to life in water typical for modern whales but unique for the Eocene cetaceans.
... 1-3). Para el presente estudio se realizaron varias visitas al lugar con la finalidad de describir el estado actual del MDPO y del material didáctico en tablas de doble entrada (Lambert et al., 2010(Lambert et al., , 2019. Se realizó un seguimiento y registro fotográfico de las actividades durante el periodo de 4 años (Tablas 2 y 3). ...
El Museo Paleontológico de Ocucaje (MDPO) se localiza en Ocucaje, Ica, Perú. Fue fundado en el 2015, por lamunicipalidad distrital, desde aquel entonces ha recibido incontables visitas de turistas, familias, escuelas y universidades. La fi nalidad de este trabajo es dar a conocer el rol educativo del Museo Didáctico Paleontológico de Ocucaje (MDPO), Ica, Perú al público en general, estudiantes, científi cos, profesores de nivel primario o secundario y docentes universitarios, y la distribución de salas y materiales educativos (Ilustraciones, maquetas, dioramas). Hasta la fecha cuenta con 5 salas de exhibición, 1 biblioteca, 26 maquetas donde destacan la especies: Cynthiacetus peruvianus Martínez-Cáceres & Muizon, 2011 (Cetacea, Basilosauridae), Ocucajea picklingi Uhen et al., 2011 (Cetacea, Basilosauridae), Livyatan melvillei Lambert et al., 2010 (Cetacea, Physeteroidea) y Odobenocetops peruvianus Muizon, 1993 (Cetacea, Odobenocetopsidae); animales extintos característicos de la región, 3 dioramas, 22 ilustraciones de los fósiles del lugar, 1 proyecto escolar y una dinámica grupal de exposición. También se reportan visitas de los estudiantes de la Universidad Ricardo Palma, Universidad Nacional de Arequipa y la Universidad Nacional Agraria la Molina, Perú. Se realizaron visitas trimestrales a lo largo de 4 años con la finalidad de describir el estado actual del MDPO y del material didáctico presente y elaborar una lista detallada de estos y proponer actividades educativas. Se concluye que el MDPO se desarrolla como un espacio de aprendizaje continuo donde los estudiantes forman parte de este de manera dinámica adquiriendo conocimiento científico actualizado.
... These movements are driven by robust axial musculature anchored to a relatively rigid torso consisting of numerous short vertebrae, and controlled by hydrofoil-like flippers [2][3][4][5][6][7]. Eocene skeletons of whales illustrate the transition from semiaquatic to aquatic locomotion, including development of a fusiform body and reduction of hindlimbs [8][9][10][11], but the rarity of Oligocene whale skeletons [12,13] has hampered efforts to understand the evolution of fluke-powered, but forelimb-controlled, locomotion. We report a nearly complete skeleton of the extinct large dolphin Ankylorhiza tiedemani comb. ...
Modern whales and dolphins are superbly adapted for marine life, with tail flukes being a key innovation shared by all extant species. Some dolphins can exceed speeds of 50 km/h, a feat accomplished by thrusting the flukes while adjusting attack angle with their flippers [1]. These movements are driven by robust axial musculature anchored to a relatively rigid torso consisting of numerous short vertebrae, and controlled by hydrofoil-like flippers [2, 3, 4, 5, 6, 7]. Eocene skeletons of whales illustrate the transition from semiaquatic to aquatic locomotion, including development of a fusiform body and reduction of hindlimbs [8, 9, 10, 11], but the rarity of Oligocene whale skeletons [12, 13] has hampered efforts to understand the evolution of fluke-powered, but forelimb-controlled, locomotion. We report a nearly complete skeleton of the extinct large dolphin Ankylorhiza tiedemani comb. n. from the Oligocene of South Carolina, previously known only from a partial rostrum. Its forelimb is intermediate in morphology between stem cetaceans and extant taxa, whereas its axial skeleton displays incipient rigidity at the base of the tail with a flexible lumbar region. The position of Ankylorhiza near the base of the odontocete radiation implies that several postcranial specializations of extant cetaceans, including a shortened humerus, narrow peduncle, and loss of radial tuberosity, evolved convergently in odontocetes and mysticetes. Craniodental morphology, tooth wear, torso vertebral morphology, and body size all suggest that Ankylorhiza was a macrophagous predator that could swim relatively fast, indicating that it was one of the few extinct cetaceans to occupy a niche similar to that of killer whales.
... On the whole the Eocene-Pliocene sedimentary succession of the East Pisco Basin represents one of the most significant marine vertebrate Lagerstätte of the Cenozoic Era due to the exceptional preservation and the elevated concentration of fossils [21,22,[40][41][42][43][44][45][46] referred to cetaceans (archaeocetes [47][48][49]; odontocetes [24,25,[50][51][52][53][54][55][56][57][58][59][60][61][62]; mysticetes [10,[63][64][65][66][67][68]), pinnipeds [69,70], marine birds [71][72][73][74], marine turtles [75], marine sloths [76][77][78][79][80][81], and sharks and rays [82][83][84][85][86][87][88]. ...
Several aspects of the fascinating evolutionary history of toothed and baleen whales (Cetacea) are still to be clarified due to the fragmentation and discontinuity (in space and time) of the fossil record. Here we open a window on the past, describing a part of the extraordinary cetacean fossil assemblage deposited in a restricted interval of time (19–18 Ma) in the Chilcatay Formation (Peru). All the fossils here examined belong to the Platanistoidea clade as here redefined, a toothed whale group nowadays represented only by the Asian river dolphin Platanista gangetica. Two new genera and species, the hyper-longirostrine Ensidelphis riveroi and the squalodelphinid Furcacetus flexirostrum, are described together with new material referred to the squalodelphinid Notocetus vanbenedeni and fragmentary remains showing affinities with the platanistid Araeodelphis. Our cladistic analysis defines the new clade Platanidelphidi, sister-group to Allodelphinidae and including E. riveroi and the clade Squalodelphinidae + Platanistidae. The fossils here examined further confirm the high diversity and disparity of platanistoids during the early Miocene. Finally, morphofunctional considerations on the entire platanistoid assemblage of the Chilcatay Formation suggest a high trophic partitioning of this peculiar cetacean paleocommunity.
... Finally, we note that the first occurrences of more specialized (more "modern-type") penguin flippers coincided with those of the earliest stem group cetaceans in the Southern Hemisphere, which were reported from the middle Eocene of Antarctica and Peru [31,32]. These toothed species may well have preyed on penguins and it is conceivable that dispersal of stem group cetaceans into the Subantarctic and Antarctic regions resulted in an increased selective pressure on the escape strategies of penguins. ...
We describe a partial skeleton of a stem group penguin from the Waipara Greensand in New Zealand, which is tentatively assigned to Muriwaimanu tuatahi. The fossil includes the first complete wing of a Paleocene penguin and informs on previously unknown features of the mandible and tibiotarsus of small-sized Sphenisciformes from the Waipara Greensand. The wing is distinguished by important features from that of all geologically younger Sphenisciformes and documents an early stage in the evolution of wing-propelled diving in penguins. In particular, the wing of the new fossil exhibits a well-developed alular phalanx and the distal phalanges are not flattened. Because the wing phalanges resemble those of volant birds, we consider it likely that the wing feathers remained differentiated into functional categories and were not short and scale-like as they are in extant penguins. Even though the flippers of geologically younger penguins may favor survival in extremely cold climates, they are likely to have been shaped by hydrodynamic demands. Possible selective drivers include a diminished importance of the hindlimbs in subaquatic propulsion, new foraging strategies (the caudal end of the mandible of the new fossil distinctly differs from that of extant penguins), or increased predation by marine mammals.
... The earliest cetaceanspakicetids, ambulocetids, and remingtonocetidsremained restricted to the Tethys (Bebej et al., 2015). Protocetids were the first whales to leave their ancestral ocean, spreading south along the coast of Africa (Gingerich and Cappetta, 2014;Gingerich and Zouhri, 2015), west across the Atlantic to North America (Geisler et al., 2005) and even South America (Lambert et al., 2019). Though geographically widespread, most protocetids retained hind limbs capable of supporting their weight on land, and thus may still have been somewhat tied to the coast (Gingerich et al., 2001). ...
The Eocene-Oligocene Southern Ocean is thought to have played a major role in cetacean evolution. Yet, fossils from its heart-Antarctica-are rare, and come almost exclusively from the Eocene La Meseta and Submeseta formations of Marambio (Seymour) Island. Here, we provide a summary and update of this crucial fossil assemblage, and discuss its relevance in the broader context of cetacean evolution. To date, Eocene specimens from Antarctica include basilosaurids, a group of archaic stem cetaceans that had already fully adapted to life in water; and the archaic toothed mysticete Llanocetus, the second oldest crown cetacean on record (ca. 34 Ma). This Eocene co-occurrence of stem and crown cetaceans is highly unusual, and otherwise only observed in Peru. Though related, at least some of the Antarctic species appear to be different from, and notably larger than their Peruvian counterparts, suggesting an early differentiation of the high latitude cetacean fauna.
There are a few mammalian lineages secondarily adapted to life in water throughout their evolutionary history. Of them, only sirenians and cetaceans evolved as fully aquatic organisms. This transition was accompanied by changes in swimming mode, from foot paddling to tail-powered propulsion, with the forelimbs acting as efficient hydrofoils and the gradual loss of external hindlimbs. Here, we describe an isolated limb from the Middle Eocene of Ukraine, 43-42 Mya, identified as a hindlimb of a fully aquatic cetacean and being the earliest cetacean reported from Europe. It is represented by flattened, jointly articulated bones, identified as the tibia and fibula with a partly reduced knee joint and loose connection to the pes, and by flattened phalanges. This anatomy reveals a hitherto only presumed cetacean morphotype, showing that some of the early fully aquatic cetaceans were four-legged animals with functional hindlimbs that could be involved in advanced styles of swimming. They used either body undulation or lift-based propulsion powered by the tail or feet and could also use a transitional swimming style combining these modes.
Soon after whales originated from small terrestrial artiodactyl ancestors, basal stem forms (archaeocetes) came to inhabit more specialized aquatic ecologies and underwent a tremendous adaptive radiation that culminated in the adoption of a fully aquatic lifestyle. This adaptive strategy is first documented by the geographically widespread extinct family Basilosauridae. Here we report a new basilosaurid genus and species, Tutcetus rayanensis, from the middle Eocene of Fayum, Egypt. This new whale is not only the smallest known basilo-saurid, but it is also one of the oldest records of this family from Africa. Tutcetus allows us to further test hypotheses regarding basilosaurids' early success in the aquatic ecosystem, which lasted into the latest Eocene, and their ability to outcompete amphibious stem whales and opportunistically adapt to new niches after they completely severed their ties to the land. Tutcetus also significantly expands the size range of the basilosaurids and reveals new details about their life histories, phylogeny, and paleobiogeography.
The quintessential example of evolutionary convergence is that between the shark, ichthyosaur, and dolphin. Although not closely related, the three exemplar taxa have independently evolved adaptations in morphology, physiology, and behavior that result in concomitant levels of performance that meet the requirements associated with operating in a dense, viscous, and thermally conductive marine environment. These apex marine predators display a remarkable amount of homoplasy. All three taxa have developed streamlined fusiform bodies to reduce drag when swimming. The position, type, and morphology of the control surfaces (i.e., fins, flippers, flukes) are similar for the convergent taxa. The control surfaces have different internal support structures, but function similarly to generate lift forces for stability and maneuverability. The main departure in control surface design among the three taxa is that dolphins lack pelvic fins. For dolphins, the loss of pelvic appendages is directly related to the possession of horizontally oriented caudal flukes, which perform double duty as a propulsive device and posterior stabilizer for trim control. The flukes of dolphins and caudal fins of ichthyosaurs and sharks have a lunate shape that function as an oscillating wing to generate high efficiency, lift-based thrust for high-speed swimming. The three convergent taxa are homeothermic, with a body temperature above that of the water in which they live. The advantages of an elevated body temperature are the attainment of higher maximum swimming speeds, longer and faster sustained swimming speeds, improved digestion, brain heating, and enhanced visual acuity. The convergence of the shark, ichthyosaur, and dolphin with respect to morphology, physiology, and locomotor performance reflects similar selective pressures imposed by the physical fluid environment that have dictated the independent evolutionary trajectories of these high-performance marine predators.
Records of aquatic mammal fossils (e.g. cetaceans, pinnipeds, sirenians, mustelids, and desmostylians) from Latin America (Mexico to Tierra del Fuego, including Antartica) span since the mid-1800s. Aquatic mammal fossils received little attention from the scientific community, with most of the first studies conducted by Northern Hemisphere researchers. Over the last 30 years, paleontological research in Latin America has increased considerably, with descriptions of several new species and revisions of published original records. The Latin American fossil record of marine mammals spans from the Eocene to the Pleistocene, with formations and specimens of global significance. All three main groups of cetaceans are represented in the continent (Archaeoceti, Mysticeti, and Odontoceti). Pinnipedia
are represented by the families Otariidae and Phocidae, with records starting in the Middle Miocene. Both living families of Sirenia (Trichechidae and Dugongidae) are recorded. While less common, but still relevant, records of desmostylians and mustelids are known from Oligocene and Miocene deposits. This review provides a summary of the aquatic mammals known to date, with a special focus on the advances and developments of the last 30 years, since Cozzuol’s (1996) review of the South American fossil record. An up-to-date complete list of species based on the literature and unpublished data is also provided. The study also provides future directions for paleontological research in Latin America, and discusses the challenges and opportunities in the field, including the emergence of a strong new generation of Latin American researchers, many of whom are women.
Nowadays, the requiem sharks comprise one of the most diverse and widespread families of selachians, i.e., Carcharhinidae. Among the carcharhinids, the genus Carcharhinus has the largest number of living species, namely, at least 35. Known from fossils as old as the Cretaceous, the requiem sharks did not significantly radiate before the Eocene (when Carcharhinus also appeared), and their diversification mainly occurred in Neogene times. Here, we describe a new species of requiem shark, Carcharhinus dicelmai sp. nov., based on fossil teeth from Lower Miocene (18.4–18.1 Ma) strata of the Chilcatay Formation of the East Pisco Basin (southern Peru). Upper teeth of C. dicelmai sp. nov. are typically provided with a slender, smooth-edged cusp; a marked coronal twist; and a distal heel that bears 1–5 coarse, angularly lobate serrae that become more prominent toward the base of the cusp. The dentition of C. dicelmai sp. nov. appears less akin to that of most other carcharhines to the cutting-clutching type, and seemingly testifies to the development of more predominantly clutching adaptations. A carcharhinid tooth from the Burdigalian to lower Langhian Cantaure Formation of Venezuela is reassigned to C. dicelmai sp. nov., suggesting a trans-Panamanian distribution for this extinct shark species.
The Cenozoic succession of the East Pisco Basin preserves the sedimentary record of several episodes of deformation of the forearc crust along the Peruvian margin. The 1:50,000 scale geological map presented here encompasses an area of about 1,000 km2 lying astride the Ica River, and contributes to our understanding of the timing and mode of basin filling and deformation. Our novel two-fold megasequence framework provides a sound basis for establishing a first-order tectono-stratigraphic setting of the mid-Eocene–upper Miocene succession exposed in the study area. We interpret that the mid-Eocene to lower Oligocene succession studied in this work (megasequence P) was deposited in a single forearc basin, which was dissected into the present-day West and East Pisco basins by a fault-bounded basement high during the late Oligocene, and subsequently overlain by the Miocene fill of the East Pisco basin (megasequence N).
The East Pisco Basin is one of the forearc basins that formed during the Cenozoic along the coast of Peru due to the subduction of the Farrallon-Nazca plate beneath the South American plate. The sedimentary fi ll of this basin is extensively exposed along the coastal Ica Desert, and includes a succession of Eocene to Pliocene marine sediments that account for a ~50-myr-long history of semi-continuous deposition. These rocks are characterized by an outstanding fossil content that remarkably contributed to our understanding of the evolutionary history of the main groups of Cenozoic marine vertebrates. In the Ica desert, the most common and signifi cant vertebrate remains belong to cetaceans. Knowledge on the fossil cetaceans of the East Pisco Basin has grown dramatically in the last fi fteen years thanks to several international research projects involving, among many others, the authors of the present article. These research eff orts have led to the discovery of several hundred fossil skeletons, the most signifi cant of which have been collected, prepared and partly published. Furthermore, interdisciplinary studies were also conducted in order to provide a high resolution chronostratigraphic framework for this fossil record. Remarkable cetacean specimens (42.6 Ma) Yumaque strata are home to the quadrupedal protocetid archaeocete Peregocetus pacifi cus, which documents the fi rst arrival of cetaceans in the Pacifi c Ocean. Geologically younger (36.4 Ma) Yumaque deposits have yielded the holotype skeleton of Mystacodon selenesis, the oldest mysticete ever found. This ancestor of the modern baleen whales had a skull provided with a complete dentition and retained hindlimbs, albeit reduced in size. In the Otuma Formation, a nine-m-long basilosaurid (Cynthiacetus peruvianus) has been discovered. The Chilcatay Formation records the fi rst great radiation of the odontocetes, represented by Inticetidae (Inticetus vertizi), basal Platanidelphidi (Ensidelphis riveroi), Squalodelphinidae (Furcacetus fl exirostrum, Huaridelphis raimondii, Macrosqualodelphis ukupachai and Notocetus vanbenedeni), Platanistidae (aff. Araeodelphis), Physeteroidea (Rhaphicetus valenciae and cf. Diaphorocetus), Chilcacetus cavirhinus, indeterminate Eurinodelphinidae, and Kentriodontidae (Kentriodon). Overall, this roughly coeval assemblage displays a considerable disparity in terms of skull shape and body size that is possibly related to the development of diff erent trophic strategies, ranging e.g., from suction to raptorial feeding. In the Pisco Formation, starting from P0, the baleen-bearing whales (Chaeomysticeti) represent the most frequent cetacean fossils (only a few mysticetes are known from the Chilcatay strata). Two chaeomysticete lineages are found in the Pisco Formation: Cetotheriidae (from Tiucetus rosae in P0 to Piscobalaena nana in P2) and Balaenopteroidea (from Pelocetus in P0 to several undescribed species of Balaenopteridae in P2, testifying to a progressive trend toward gigantism). Odontocetes are rare in P0, the "kentriodontid" Incacetus broggii being the only species described from these strata, but they become more abundant and diverse in P1 and P2. In P1, the commonest toothed whale is Messapicetus gregarius, a member of Ziphiidae featuring an extremely elongated rostrum and a complete set of functional teeth. Another ziphiid from P1 is Chimuziphius coloradensis, known only from the fragmentary holotype cranium. The P1 strata also record the appearance of the crown Delphinida, with the superfamily Inioidea being represented by two small pontoporiids (Brachydelphis mazeasi and Samaydelphis chacaltanae) and one iniid (Brujadelphis ankylorostris). Moreover, P1 is also home to the stem physeteroid Livyitan melvillei; featuring a three-m-long skull and teeth reaching 36 cm in length, L. melvillei was one of the largest raptorial predators and, possibly, the biggest tetrapod bite ever found. Acrophyseter is another macroraptorial sperm whale, distinctly smaller than L. melvillei, known from both P1 and P2. Even smaller in size are the kogiids Platyscaphokogia landinii and Scaphokogia cochlearis, both of which are known from the upper strata of P2. The same allomember is also home to the ziphiids Chavinziphius maxillocristatus and Nazcacetus urbinai, the "kentriodontids" Atocetus iquensis and Belenodelphis peruanus, and undescribed members of Phocoenidae.
Body sizes of marine amniotes span six orders of magnitude, yet the factors that governed the evolution of this
diversity are largely unknown. High primary production of modern oceans is considered a prerequisite for the
emergence of cetacean giants, but that condition cannot explain gigantism in Triassic ichthyosaurs. We
describe the new giant ichthyosaur Cymbospondylus youngorum sp. nov. with a 2-meter-long skull from the
Middle Triassic Fossil Hill Fauna of Nevada, USA, underscoring rapid size evolution despite the absence of many
modern primary producers. Surprisingly, the Fossil Hill Fauna rivaled the composition of modern marine
mammal faunas in terms of size range, and energy-flux models suggest that Middle Triassic marine food webs
were able to support several large-bodied ichthyosaurs at high trophic levels, shortly after ichthyosaur origins.
Global sea-level changes and substantial vertical displacement along the Monte Grande Fault (MGF) in the lower Río Ica Valley of south-central Peru influenced the accumulation of bioclast-bearing and diatom-bearing Miocene siliciclastic sediments in an area of the East Pisco forearc basin (EPB) colloquially known as Laberinto. Two depositional hiatuses in the Laberinto area (~17–14 Ma, ~12.5–10 Ma) manifest as sediment-filled erosional depressions a few kilometers in breadth. Erosion of the older
depression was preceded by an ~18-Ma massive debris flow, possibly triggered by motion on the MGF causing lower Miocene lithoclastic olistoliths of up to two hundred meters length to spill off the footwall
block. Sediment shed from the same footwall block may have formed previously recognized early Miocene deltas. From 14–13 Ma, the older depression filled with sediments herein assigned to the provisionally named Laberinto, Pampa, and Naranja members of the Pisco Formation, the latter member being characterized by marine delta foreset beds. The three members are at least partly correlative with the Pisco-0 sequence of the Pisco Formation. The younger depression was overrun at 10 Ma by debris flows of lithoclastic and granitic cobbles and boulders, then filled with diatomaceous silty sand with five-meter-sized lithoclastic olistoliths. The two lithologies constitute the provisionally named Mature Formation. Radiometric and newly revised biochronological data from throughout the EPB coupled with new diatom data from the Laberinto area have provided new insights into the correlation of sequences
within the Chilcatay and Pisco formations and the interaction of local and basin-wide tectonism and
global eustatic sea-level events across the basin.
Background
Basilosaurid archaeocetes are known from the Late Eocene of virtually all coastlines bearing coeval marine rocks except the North Pacific Basin, until now. Here we report on three consecutive posterior thoracic vertebrae of a large, basilosaurid archaeocete from a Late Eocene horizon in the Keasey Formation in Oregon.
Methods
These vertebrae were morphologically and morphometrically compared to other vertebrae of similar age from around the world.
Results
The specimens were determined to be different from all currently named species of fossil cetacean, but most similar to those found in the Gulf Coast region of North America. These vertebrae represent the first confirmed specimen of a Late Eocene basilosaurid from the North Pacific. These and other basilosaurids known only from vertebrae are reviewed here in the context of Late Eocene paleoceanography and cetacean evolution.
Biogeographical distributional patterns of cetaceans reflect dispersal events and colonization of the oceans from their ancestral area in the ancient Sea of Tethys~53 Ma. Likewise, they reveal several vicariance events throughout the evolutionary history of this group. However, our understanding of how these processes took place and what biogeographical scenarios occurred among the different groups of cetaceans through time is limited. Consequently, this work focuses on explaining the distributional patterns of the well-known North Pacific toothed mysticetes, Aetiocetidae, through the power of retrodiction offered by track analysis (panbiogeography) and cladistic biogeography, using the approach of evolutionary biogeography. Our results show that the distributional patterns of Aetiocetidae explain their endemism in the North Pacific, as well as indicating that their hypothetical ancestor probably colonized the Pacific from the Atlantic Ocean by a dispersal event (founder effect) via the Central American Seaway. Furthermore, their biogeographical history shows that the adaptive radiation (cladogenesis) of Aetiocetidae is the result of peripatric speciation followed by sympatric speciation within a heterogeneous environment. Finally, the biogeographical framework of Aetiocetidae further supports the relevant role that the Pacific Ocean has played in the evolution of Oligocene cetaceans as a geographical area that promoted endemism, dispersal and colonization. At more local scales, environmental conditions further promoted increased diversity and disparity amongst Mysticeti.
Lepidocyclinids are one of the most common group of Cenozoic large benthic foraminifera and, thanks to their clear evolutionary patterns, they are extensively used in biostratigraphy. They originated during the Eocene in the American region and then spread eastward, reaching a worldwide distribution in the Oligocene. This paper investigates the southernmost population of lepidocyclinids ever found along the Pacific coast of South America, located in the lower part of the Paracas Formation (Los Choros Member) of the East Pisco Basin of Peru. The examined Los Choros strata are composed of mixed siliciclastic-bioclastic coarse-grained deposits. The skeletal assemblage is dominated by large benthic foraminifera and mollusks with subordinate echinoids and barnacles, suggesting a deposition in a shallow, tropical, shelf environment with a moderate nutrient supply. The large benthic foraminiferal assemblage is largely dominated by Lepidocyclina rdouvillei. This species is extremely primitive, exhibiting ancestral characters such as a straight wall separating the protoconch and deuteroconch, very large principal auxiliary chambers and a poorly organized equatorial plane. The presence of common and primitive L. rdouvillei, supported by the associated occurrence of Polylepidina, suggests an age comprised between 43.6 Ma and 40.5 Ma for the Los Choros Member in the study area. This range is confirmed by nannofossil assemblages that indicate an age between 42.37 Ma and 40.34 Ma for the base of the overlying Yumaque Member of the Paracas Formation. These results highlight the potential of lepidocyclinids for biostratigraphy and paleoenvironmental reconstructions in South America.
Cetaceans constitute a textbook example of the secondary adaptation of tetrapods to aquatic life. This major event in the evolutionary history of mammals is often linked in the literature to the limb‐to‐fin transition. Paradoxically, limb bones are scarce in the fossil record of early cetaceans, and the transition from a limb‐adapted morphology for an amphibious life in shallow water to a fin‐adapted morphology for a pelagic lifestyle remains poorly documented. Here, we describe new protocetid remains from the upper Lutetian of Senegal, including a nearly complete articulated forelimb. A cladistic analysis including 24 taxa and 137 morphological characters recovers the new African specimen close to Carolinacetus. It also confirms that cetacean dispersal to the New World was not the result of a single colonization event. A 3D model of the forelimb was reconstructed. Anatomical comparisons suggest that it is unlikely that the Senegalese forelimb was used as a rigid pectoral flipper for steering as in basilosaurids and modern cetaceans. Instead, we suggest that the hand was actively used during swimming. This challenges previous reconstructions of protocetids as mainly foot‐powered swimmers, and suggests that swimming specializations of early cetaceans were probably more diverse than previously considered.
Extant cetaceans are fully aquatic mammals with deep modifications of their sensory organs, notably of the sound perception pathway. Early diverging cetaceans, known as archaeocetes, show a diversity of morphologies of the petrotympanic complex and middle ear ossicles, documenting a variety of sound transmission mechanisms from a mostly terrestrial configuration to a fully aquatic layout. Protocetids are a paraphyletic assemblage of semi-aquatic archaeocetes known from the Eocene. The auditory region of these ‘transitional’ forms is only partly known. The middle Eocene locality of Kpogamé, Togo (46–43 Ma) has yielded abundant material of protocetid whales documenting the auditory region, including isolated bullae, one petrosal and a skull fragment preserving the petrotympanic complex. Detailed study of this material leads us to reassess the original taxonomic attribution of this material, first attributed to Togocetus traversei, and to recognize three different protocetid taxa on the basis of bullar and petrosal remains: ?Carolinacetus sp., Togocetus traversei and Protocetidae indeterminate (morphotype γ). Associating isolated petrosals or bullae with dental remains solely based on size criteria can be misleading and we show here that there is no correlation between the size of tympanic bulla and size of dental remains in protocetids. CT-scan investigation of the in situ petrotympanic complex reveals that Protocetidae retained a complete tympanic ring similar to that of terrestrial artiodactyls and that the involucrum could probably articulate with the medial side of the ventral surface of the petrosal. This bulla/petrosal articulation is absent in fully aquatic cetaceans. Finally, the close phylogenetic relationships between protocetids from Kpogamé and North American protocetids suggest successive dispersals of these non-fully aquatic archaeocetes from African coasts to North America.
The sequence stratigraphic framework and a summary of the fossil fauna of the Upper Miocene
portion of the Pisco Formation exposed along the western side of the Ica River (southern Peru) is presented
through a new geological map encompassing an area of about 200 km2
and detailed chronostratigraphic analyses.
Extensive ield mapping and sedimentological study of outcrop sections have shown that the Pisco Formation is
a cyclical sediment unit composed of at least three ining-upward, unconformity-bounded depositional sequences,
designated P0, P1, and P2 from oldest to youngest. In the study area, these sequences progressively onlap a composite
basal unconformity from southwest to northeast.
Integration of biostratigraphic and tephrochronologic age determinations constrains the ages of the three
Pisco sequences within the study area. Based on the age of surrounding sediments, a conservative estimate of
the age of P0 suggests deposition of these strata between 17.99 ± 0.10 Ma and 9.00 ± 0.02 Ma, whereas diatom
biostratigraphy and calculated 40Ar/39Ar ages converge to indicate that strata of the P1 sequence were deposited
sometime between 9.5 Ma and 8.9 Ma and that those of the P2 sequence are younger than 8.5 Ma and older than
6.71 ± 0.02 Ma. Our survey for both vertebrate and macro-invertebrate remains in the three sequences conirms
the outstanding paleontological value of the Pisco Formation and contributes to depict regional faunal shifts in the
fossil assemblage.
Remingtonocetidae are Eocene archaeocetes that represent a unique experiment in cetacean evolution. They possess long narrow skulls, long necks, fused sacra, and robust hind limbs. Previously described remingtonocetids are known from middle Eocene Lutetian strata in Pakistan and India. Here we describe a new remingtonocetid, Rayanistes afer, n. gen. n. sp., recovered from a middle to late Lutetian interval of the Midawara Formation in Egypt. The holotype preserves a sacrum with four vertebral centra; several lumbar and caudal vertebrae; an innominate with a complete ilium, ischium, and acetabulum; and a nearly complete femur. The ilium and ischium of Rayanistes are bladelike, rising sharply from the body of the innominate anterior and posterior to the acetabulum, and the acetabular notch is narrow. These features are diagnostic of Remingtonocetidae, but their development also shows that Rayanistes had a specialized mode of locomotion. The expanded ischium is larger than that of any other archaeocete, supporting musculature for powerful retraction of the hind limbs during swimming. Posteriorly angled neural spines on lumbar vertebrae and other features indicate increased passive flexibility of the lumbus. Rayanistes probably used its enhanced lumbar flexibility to increase the length of the power stroke during pelvic paddling. Recovery of a remingtonocetid in Egypt broadens the distribution of Remingtonocetidae and shows that protocetids were not the only semiaquatic archaeocetes capable of dispersal across the southern Tethys Sea.
An integrated stratigraphy is established for the middle Ypresian of the Mons Basin (southwest Belgium), based on evidence from Mont Panisel borehole. The Mont-Panisel succession comprises representatives of the Mons-en-Pevele Sand Formation overlain by the Hyon Sand Formation. The latter is subdivided into a lower Bois-la-Haut Sand Member and an upper Mont-Panisel Sand Member. A sequence-stratigraphic interpretation of the Mont-Panisel succession is attempted, and regional correlations are proposed with central and northwest Belgium and the Paris Basin. -from Authors
Six genera and species of archaic whales are present in a new fauna from the Aridal Formation at Gueran in the Sahara Desert of southwestern Morocco. Three of the archaeocete species represent semiaquatic Protocetidae and three species are fully aquatic Basilosauridae. Protocetids are characteristic of Lutetian lower middle Eocene strata, and basilosaurids are characteristic of Priabonian late Eocene beds. Similar representation of both families is restricted to intervening Bartonian strata and indicative of a late middle Eocene age. Archaeocetes from Gueran include (1) a small protocetid represented by a partial humerus, teeth, and vertebrae; (2) a middle-sized protocetid represented by a partial innominate and proximal femur; (3) the very large protocetid Pappocetus lugardi represented by teeth, a partial innominate, and two partial femora; (4) a new species of the small basilosaurid Chrysocetus represented by a dentary, teeth, humeri, and many vertebrae; (5) a new species of the larger basilosaurid Platyosphys (resurrected as a distinct genus) represented by a partial braincase, tympanic bulla, and many vertebrae; and (6) the large basilosaurid Eocetus schweinfurthi represented by teeth, a tympanic bulla, and lumbar vertebrae. The Gueran locality is important geologically because it constrains the age of a part of the Aridal Formation, and biologically because it includes a diversity of archaic whales represented by partial skeletons with vertebrae in sequence and by forelimb and hind limb remains. With further collecting, Gueran archaeocete skeletons promise to clarify the important evolutionary transition from foot-powered swimming in Protocetidae to the tail-powered swimming of Basilosauridae and all later Cetacea.
SYNOPSIS. The evolution of fully aquatic mammals from quadrupedal, terrestrial mammals was associated with changes in morphology and swimming mode. Drag is minimized by streamlining body shape and appendages. Improvement in speed, thrust production and efficiency is accomplished by a change of swimming mode. Terrestrial and semiaquatic mammals employ drag-based propulsion with paddling appendages, whereas fully aquatic mammals use lift-based propulsion with oscillating hydrofoils. Aerobic efficiencies are low for drag-based swimming, but reach a maximum of 30% for lift-based propulsion. Propulsive efficiency is over 80% for lift-based swimming while only 33% for. paddling. In addition to swimming mode, the transition to high performance propulsion was associated with a shift from surface to submerged swimming providing a reduction in transport costs. The evolution of aquatic mammals from terrestrial ancestors required increased swimming performance with minimal compromise to terrestrial movement. Examination of modern analogs to transitional swimming stages suggests that only slight modification to the neuromotor pattern used for terrestrial locomotion is required to allow for a change to lift-based propulsion.
The gross morphology of the axial postcranium of Thalassocnus is presented here, completing the description of the skeleton of the genus. Thalassocnus is characterized by a low spinous process on C7, a cranially shifted position of the diaphragmatic vertebra, a great number of caudal vertebrae, the morphology of their transverse processes, and the conservation of the craniocaudal length of their centra up to Ca19. Additionally, the late species of Thalassocnus feature cranial articular surfaces of the atlas that are oriented cranioventrally and thoracolumbar vertebrae with spinous processes that are more inclined caudally, shorter craniocaudally, and have a smaller apex than in earlier species. In the late species, the thoracolumbar vertebrae are also characterized by zygapophyseal articulations that are more conspicuously concavo-convex, and by ribs that are affected by osteosclerosis and pachyostosis. Thalassocnus yaucensis additionally differs from the earlier species of the genus in featuring thoracolumbar vertebral centra that are shortened craniocaudally. The morphology of the axial postcranium of Thalassocnus is consistent with a reduced amount of time spent in a terrestrial habitat. Furthermore, the overall body size and extensive and extreme osteosclerosis of Thalassocnus suggest that bottom-walking was part of its modes of swimming. The tail was probably involved in diving and equilibration but did not contribute to propulsion. A downturned position of the head is inferred for the late species of Thalassocnus, and is probably related to grazing activity on the seafloor. The stabilized vertebral column may be related to the digging behavior purported in Thalassocnus. The aquatic functions of the entire skeleton of Thalassocnus are reviewed.
Lutetian lower middle Eocene phosphate deposits of Kpogame-Hahotoe in Togo yield new information about whales and sea cows in West Africa. Most specimens are individual teeth and bones, collected as isolated elements, but some appear to have been associated. Most are conservatively interpreted to represent a new 300-400 kg protocetid archaeocete, Togocetus traversei. This genus and species is distinctly primitive for a protocetid in retaining a relatively small mandibular canal in the dentary and retaining a salient metaconid on the lower first molar (M-1), but it is derived relative to earlier archaeocetes in having large, dense, osteosclerotic tympanic bullae. Mandibular canal size and large dense bullae are not as tightly linked in terms of function in hearing as previously thought. Postcranially Togocetus traversei had many characteristics found in other semiaquatic protocetids: a relatively long neck, mobile shoulder, digitigrade manus, large pelvis, well-developed hind limbs; and feet specialized for swimming. Loss of a fovea on the head of the femur indicates loss of the teres ligament stabilizing the hip, which is a derived specialization consistent with life in water. Protocetid specimens distinctly smaller and larger than those of Togocetus traversei indicate the presence of at least three protocetids at Kpogame. Sirenian vertebral and rib pieces indicate the presence of a protosirenid and a dugongid. Finally, a vertebral centrum and piece of humerus appear to represent a large land mammal. A diverse fauna of archaic whales and early sirenians inhabited the western margin of Africa and the eastern Atlantic Ocean as early as 46-44 million years before present, showing that both cetaceans and sirenians were widely distributed geographically by this time.
Three new specimens of middle Eocene cetaceans are reported from the Pisco Basin of southern Peru. All three specimens originate from the Paracas Formation and their minimum age is constrained to about 37 Ma using 40 Ar/ 39 Ar dating of ash collected ∼100 m up section from the source localities. Two new genera of archaeocete cetaceans are described along with additional material of another distinctive protocetid, which is not named pending the discovery of more complete material. Phylogenetic analysis resolves the two new genera within Basilosauridae, while the unnamed protocetid is closely related to Eocetus. The discovery of crownward protocetids in South America demonstrates that early cetaceans may have dispersed into both hemispheres prior to evolving a fully aquatic lifestyle. Geochronologic constraints on the age of new Peruvian archaeocetes establish them as the oldest whales from South America and among the oldest known from the Southern Hemisphere, which highlights the need for better sampling of marginal marine rocks from this part of the world.
A shallow-marine fossil biota was recovered from the Blue Bluff unit (formerly part of the McBean Formation) in the Upper Coastal Plain of eastern Georgia. Biochronologically significant mollusks (e.g., Turritella nasuta, Cubitostrea sellaeformis, Pteropsella lapidosa) and calcareous nannoplankton (e.g., Chiasmolithus solitus, Reticulofenestra umbilica, Cribocentrum reticulatum) indicate a latest Lutetian-earliest Bartonian age, or about 40 to 41 Ma. Georgiacetus vogtlensis new genus and species is described
from a well-preserved, partial skeleton. Georgiacetus s the oldest known whale with a true pterygoid sinus fossa in its basicranium and a pelvis that did not articulate directly with the sacral vertebrae, two features whose acquisitions were important steps toward adaptationto a fully marine existence. The posterior four cheek teeth of G. vogtlensis form a series of carnassial-like shearing blades. These teeth also bear small, blunt accessory cusps, which are regarded as being homologous with the larger, sharper accessory cusps
of basilosaurid cheek teeth.
A docodontan mammaliaform from the Middle Jurassic of China possesses swimming and burrowing skeletal adaptations and some dental features for aquatic feeding. It is the most primitive taxon in the mammalian lineage known to have fur and has a broad, flattened, partly scaly tail analogous to that of modern beavers. We infer that docodontans were semiaquatic, convergent to the modern platypus and many Cenozoic placentals. This fossil demonstrates that some mammaliaforms, or proximal relatives to modern mammals, developed diverse locomotory and feeding adaptations and were ecomorphologically different from the majority
of generalized small terrestrial Mesozoic mammalian insectivores.
A new protocetid archaeocete, Aegyptocetus tarfa, is represented by a nearly complete cranium and an associated partial skeleton. The specimen was recovered when marbleized limestone was imported commercially to Italy and cut into decorative facing stone. It came from middle Eocene Tethyan marine strata of the Gebel Hof Formation of Wadi Tarfa in the Eastern Desert of Egypt. Exceptional preservation and preparation enables study of some internal features of the skull as well as its external morphology. The skull of Aegyptocetus is unusual in having the rostrum and frontal portions of the cranium deflected more ventrally relative to the braincase than is typical for archaeocetes. This ventral deflection, clinorhynchy, is a rare specialization related to feeding or hearing that is widely distributed across mammals. Aegyptocetus has well-developed ethmoidal turbinal bones, indicating retention of a functional sense of smell. It also has cranial asymmetry, thinning of the lateral walls of the dentaries, enlarged mandibular canals, and thinning of the anterolateral walls of the tympanic bullae, indicating enhanced ability to hear in water. Neural spines are long on thoracic vertebrae T1 through T8, suggesting that Aegyptocetus was able to support its weight on land like other protocetids. This combination of terrestrial and aquatic characteristics is consistent with interpretation of protocetids as semiaquatic. The pattern of tooth marks preserved on the ribs of Aegyptocetus indicates that the individual studied here was attacked by a large shark, but it is not certain whether this was the cause of death.
SYNOPSIS. The evolution of fully aquatic mammals from quadrupedal, terrestrial mammals was associated with changes in morphology and swimming mode. Drag is minimized by streamlining body shape and appendages. Improvement in speed, thrust production and efficiency is accomplished by a change of swimming mode. Terrestrial and semiaquatic mammals employ drag-based propulsion with paddling appendages, whereas fully aquatic mammals use lift-based propulsion with oscillating hydrofoils. Aerobic efficiencies are low for drag-based swimming, but reach a maximum of 30% for lift-based propulsion. Propulsive efficiency is over 80% for lift-based swimming while only 33% for paddling. In addition to swimming mode, the transition to high performance propul- sion was associated with a shift from surface to submerged swimming providing a reduction in transport costs. The evolution of aquatic mam- mals from terrestrial ancestors required increased swimming performance with minimal compromise to terrestrial movement. Examination of mod- ern analogs to transitional swimming stages suggests that only slight mod- ification to the neuromotor pattern used for terrestrial locomotion is re- quired to allow for a change to lift-based propulsion.
The propulsive swimming modes of river otters (Lutra canadensis) were examined relative to behavior. Six river otters were filmed in zoo enclosures that provided surface or sub- merged views. The repertoire of swimming modes observed for otters included quadrupedal paddling, forelimb paddling, alternate hind-limb paddling, simultaneous hind-limb pad- dling, and body and tail dorsoventral undulation. Paddling modes accounted for 88% of surface swimming observations and for 86% of observations involving submerged maneu- vers. Dorsoventral undulation predominated during rectilinear submerged swimming. Tran- sition from paddling to undulatory propulsion was accomplished by use of simultaneous hind-limb paddling in concert with dorsoventral body and tail flexion. These motions produced a posteriorly directed traveling wave in the tail with an average velocity 1.62 times the swimming velocity. The higher velocity in the tail could produce hydrodynamic thrust during all phases of the paddling cycle.
Major and trace element, U-Pb zircon geochronology and Pb-isotopic data are presented on plutons from the San Nicolás batholith of central and southern Peru.
The major oxides of 9 samples indicate a high-K calc-alkaline trend, and trace element discriminant diagrams reveal affinities to volcanic arc or late- to post-collision calc-alkaline intrusions. The apparent contradiction implied by the Rb-Hf-Ta triangular diagram (within-plate) strongly suggests loss of Rb, an interpretation supported by the extensive deuteric alteration and sericitization of feldspar. Ta/Zr, Ta/Hf and Ta/Nb ratios are considerably higher than those of volcanic arc intrusions, and favour the late or post-collision calc-alkaline classification.
U-Pb zircon geochronology shows that the San Nicolás batholith was emplaced in two short-lived magmatic events at approximately 425 Ma and 394-388 Ma ago. The presence of an inherited component of radiogenic Pb of Precambrian age in the zircons suggests xenocrystic cores, which were most likely scavenged from Precambrian basement rocks of the Arequipa massif.
Time-adjusted Pb isotopic compositions of feldspars have the following ranges: ²⁰⁶ Pb/ ²⁰⁴ Pb = 17.798-18.272, ²⁰⁷ Pb/ ²⁰⁴ Pb = 15.571-15.626, and ²⁰⁸ Pb/ ²⁰⁴ Pb = 38.182-38.291, indicating that Precambrian basement was incorporated into the magmas of the batholith. Other components are believed to have originated in an ‘enriched’ upper mantle or lower crustal wedge pervasively metasomatized by fluids extracted largely from subducted sediments.
U-Pb zircon age distribution, trace element characteristics and the linear nature of the plutons firmly establish the San Nicolás batholith as the plutonic substructure of an early Palaeozoic continental arc, which may extend northwards in Peru and southwards
GROUND sloths (Gravigrada, Xenarthra) are known from middle or
late Oligocene to late Pleistocene in South America1 and from
late Miocene to late Pleistocene in North America2. They are
medium to gigantic in size and have terrestrial3 habits.
Discovery of abundant and well preserved remains of a new sloth
(Thalas-socnus natans), in marine Pliocene deposits from
Peru46 drastically expands our knowledge of the range of
adaptation of the order. The abundance of individuals, the absence of other
land mammals in the rich marine vertebrate fauna of the site5,6,
and the fact that the Peruvian coast was a desert during the
Pliocene7,8 suggest that it was living on the shore and entered
the water probably to feed upon sea-grasses or seaweeds. The morphology of
premaxillae, femur, caudal vertebrae (similar to those of otters and beavers)
and limb proportions are in agreement with this interpretation.
A new genus and species of protocetid cetacean, Carolinacetus gingerichi, is described from a partial skull, the posterior portion of both dentaries, 13 vertebrae, and elements of 15 ribs found in the Cross Member of the late middle Eocene Tupelo Bay Formation in Berkeley County, South Carolina. That formation is also defined and named in this paper. Although the holotype skull of Carolinacetus is fragmentary, it includes the best preserved petrosal of any described specimen from the archaeocete families of Pakicetidae, Ambulocetidae, Remingtonocetidae, and Protocetidae. The phylogenetic relationships of Carolinacetus were determined by a cladistic analysis of a dataset that includes 16 cetacean taxa and 5 outgroups scored for 107 morphological characters. Carolinacetus was found to be the basalmost cetacean known from North America, and the most conspicuous character supporting this position is the external, bony nares being anterior to P1. Other noteworthy findings are that Georgiacetus is more basal than Babiacetus and that Remingtonocetidae occupies a branch between Pakicetidae and Protocetidae. Based on our phylogenetic analysis, the genus Gaviacetus is removed from the Basilosauridae and restored to the Protocetidae. Possible dispersal routes of protocetids from the Old World to the New World are discussed, and a route westward along the southern coast of Greenland is considered to be the most likely avenue of protocetid migration to North America.
The energetics and hydrodynamics of surface and submerged swimming were compared in the sea otter (Enhydra lutris).1.
Sea otters used two distinct speed ranges that varied with swimming mode. Sustained surface swimming was limited to speeds less than 0.80 m/s, while sustained submerged swimming occurred over the range of 0.60 to 1.39 m/s.
2.
Rates of oxygen consumption (VO2) at the transition speed (0.80 m/s) were 41% lower for submerged swimming by sea otters in comparison to surface swimming.
3.
Total cost of transport for surface swimming sea otters, 12.56 joules/kgsm, was more than 12 times the predicted value for a similarly-sized salmonid fish. Transport costs for submerged swimming at the same speed was only 7.33 times the predicted value.
4.
The allometric relationship for minimum cost of transport in surface swimming birds and mammals wasy=23.87x–0.15 wherey=cost of transport in joules/kgm andx=body mass in kg. This regression loosely parallels the relationship for salmonid fish.
5.
Correlations between aquatic behavior, morphological specialization, and swimming energetics indicate that the development of swimming in mustelids involved transitions from fore-paw to hindpaw propulsion, and from surface to submerged swimming.
The long-term isolation of South America during most of the Cenozoic produced a highly peculiar terrestrial vertebrate biota, with a wide array of mammal groups, among which caviomorph rodents and platyrrhine primates are Mid-Cenozoic immigrants. In the absence of indisputable pre-Oligocene South American rodents or primates, the mode, timing and biogeography of these extraordinary dispersals remained debated. Here, we describe South America's oldest known rodents, based on a new diverse caviomorph assemblage from the late Middle Eocene (approx. 41 Ma) of Peru, including five small rodents with three stem caviomorphs. Instead of being tied to the Eocene/Oligocene global cooling and drying episode (approx. 34 Ma), as previously considered, the arrival of caviomorphs and their initial radiation in South America probably occurred under much warmer and wetter conditions, around the Mid-Eocene Climatic Optimum. Our phylogenetic results reaffirm the African origin of South American rodents and support a trans-Atlantic dispersal of these mammals during Middle Eocene times. This discovery further extends the gap (approx. 15 Myr) between first appearances of rodents and primates in South America.
Protocetidae are middle Eocene (49-37 Ma) archaeocete predators ancestral to later whales. They are found in marine sedimentary rocks, but retain four legs and were not yet fully aquatic. Protocetids have been interpreted as amphibious, feeding in the sea but returning to land to rest.
Two adult skeletons of a new 2.6 meter long protocetid, Maiacetus inuus, are described from the early middle Eocene Habib Rahi Formation of Pakistan. M. inuus differs from contemporary archaic whales in having a fused mandibular symphysis, distinctive astragalus bones in the ankle, and a less hind-limb dominated postcranial skeleton. One adult skeleton is female and bears the skull and partial skeleton of a single large near-term fetus. The fetal skeleton is positioned for head-first delivery, which typifies land mammals but not extant whales, evidence that birth took place on land. The fetal skeleton has permanent first molars well mineralized, which indicates precocial development at birth. Precocial development, with attendant size and mobility, were as critical for survival of a neonate at the land-sea interface in the Eocene as they are today. The second adult skeleton is the most complete known for a protocetid. The vertebral column, preserved in articulation, has 7 cervicals, 13 thoracics, 6 lumbars, 4 sacrals, and 21 caudals. All four limbs are preserved with hands and feet. This adult is 12% larger in linear dimensions than the female skeleton, on average, has canine teeth that are 20% larger, and is interpreted as male. Moderate sexual dimorphism indicates limited male-male competition during breeding, which in turn suggests little aggregation of food or shelter in the environment inhabited by protocetids.
Discovery of a near-term fetus positioned for head-first delivery provides important evidence that early protocetid whales gave birth on land. This is consistent with skeletal morphology enabling Maiacetus to support its weight on land and corroborates previous ideas that protocetids were amphibious. Specimens this complete are virtual 'Rosetta stones' providing insight into functional capabilities and life history of extinct animals that cannot be gained any other way.
Modern members of the mammalian order Cetacea (whales, dolphins and porpoises) are obligate aquatic swimmers that are highly distinctive in morphology, lacking hair and hind limbs, and having flippers, flukes, and a streamlined body. Eocene fossils document much of cetaceans' land-to-water transition, but, until now, the most primitive representative for which a skeleton was known was clearly amphibious and lived in coastal environments. Here we report on the skeletons of two early Eocene pakicetid cetaceans, the fox-sized Ichthyolestes pinfoldi, and the wolf-sized Pakicetus attocki. Their skeletons also elucidate the relationships of cetaceans to other mammals. Morphological cladistic analyses have shown cetaceans to be most closely related to one or more mesonychians, a group of extinct, archaic ungulates, but molecular analyses have indicated that they are the sister group to hippopotamids. Our cladistic analysis indicates that cetaceans are more closely related to artiodactyls than to any mesonychian. Cetaceans are not the sister group to (any) mesonychians, nor to hippopotamids. Our analysis stops short of identifying any particular artiodactyl family as the cetacean sister group and supports monophyly of artiodactyls.
Partial skeletons of two new fossil whales, Artiocetus clavis and Rodhocetus balochistanensis, are among the oldest known protocetid archaeocetes. These came from early Lutetian age (47 million years ago) strata in
eastern Balochistan Province, Pakistan. Both have an astragalus and cuboid in the ankle with characteristics diagnostic of
artiodactyls; R. balochistanensis has virtually complete fore- and hind limbs. The new skeletons are important in augmenting the diversity of early Protocetidae,
clarifying that Cetacea evolved from early Artiodactyla rather than Mesonychia and showing how early protocetids swam.
New specimens of middle Eocene Basilosaurus isis from Egypt include the first functional pelvic limb and foot bones known in Cetacea. These are important in corroborating the intermediate evolutionary position of archaeocetes between generalized Paleocene land mammals that used hind limbs in locomotion and Oligocene-to- Recent whales that lack functional pelvic limbs. The foot is paraxonic, consistent with derivation from mesonychid Condylarthra. Hind limbs of Basilosaurus are interpreted as copulatory guides.
Although the first ten million years of whale evolution are documented by a remarkable series of fossil skeletons, the link to the ancestor of cetaceans has been missing. It was known that whales are related to even-toed ungulates (artiodactyls), but until now no artiodactyls were morphologically close to early whales. Here we show that the Eocene south Asian raoellid artiodactyls are the sister group to whales. The raoellid Indohyus is similar to whales, and unlike other artiodactyls, in the structure of its ears and premolars, in the density of its limb bones and in the stable-oxygen-isotope composition of its teeth. We also show that a major dietary change occurred during the transition from artiodactyls to whales and that raoellids were aquatic waders. This indicates that aquatic life in this lineage occurred before the origin of the order Cetacea.
We describe Tupelocetus palmeri, a new genus and species of archaeocete whale, based on a single specimen from the Cross Member of the middle Eocene Tupelo Bay Formation (Bartonian). The holotype consists of a partial cranium with complete petrosals, posterior processes of tympanics, the posterior ends of the nasals, a part of the right orbit, and what are interpreted as the right and left P2s. The incomplete skull was collected from the Martin Marietta Cross Quarry (Berkeley County, South Carolina), which has also furnished the holotype of Carolinacetus gingerichi. The new species differs from all other protocetids in having a deep cavity on the occiput, as well as having the following combination of features: large nasal processes of frontals, single-cusped P2, and premaxilla terminates at level of P2 or P3. A phylogenetic analysis places T. palmeri in a large polytomy along the cetacean stem, more closely related to crown Cetacea than Maiacetus, Artiocetus, and Rodhocetus, but more basal than Georgiacetus, Babiacetus, and Eocetus. Another member of this polytomy is Natchitochia jonesi, and although specimens of Natchitochia and T. palmeri do not share any elements, what is preserved suggests that they are similar in size and among the largest of all protocetids. Although we are unable to differentiate these two species, we outline future data that could resolve this question.
Although combined molecular and morphological analyses point to a late middle Eocene (38-39 million years ago) origin for the clade Neoceti (Odontoceti, echolocating toothed whales plus Mysticeti, baleen whales, and relatives), the oldest known mysticete fossil dates from the latest Eocene (about 34 million years ago) of Antarctica [1, 2]. Considering that the latter is not the most stemward mysticete in recent phylogenies and that Oligocene toothed mysticetes display a broad morphological disparity most likely corresponding to contrasted ecological niches, the origin of mysticetes from a basilosaurid ancestor and its drivers are currently poorly understood [1, 3-8]. Based on an articulated cetacean skeleton from the early late Eocene (Priabonian, around 36.4 million years ago) of the Pisco Basin, Peru, we describe a new archaic tooth-bearing mysticete, Mystacodon selenensis gen. et sp. nov. Being the geologically oldest neocete (crown group cetacean) and the earliest mysticete to branch off described so far, the new taxon is interpreted as morphologically intermediate between basilosaurids and later toothed mysticetes, providing thus crucial information about the anatomy of the skull, forelimb, and innominate at these critical initial stages of mysticete evolution. Major changes in the morphology of the oral apparatus (including tooth wear) and flipper compared to basilosaurids suggest that suction and possibly benthic feeding represented key, early ecological traits accompanying the emergence of modern filter-feeding baleen whales' ancestors.
The Mio-Pliocene Pisco Formation, Peru, is a world renowned Konservat-Lagerstätte. Beside its potential in preserving important information on the history of the Pacific Ocean during the Miocene, the Pisco Fm. provides palaeontologists with the unique opportunity to study in detail the evolution of marine vertebrate fauna during the Neogene. Because diatomites are one of the main lithologies of the Pisco Fm., previous authors have hypothesised exceptionally high sedimentation rates related to the deposition of diatom frustules as the main cause leading to the formation of the Lagerstätte. However, sedimentation rates were never calculated. With the perspective to build a solid stratigraphic framework for the whole Pisco Fm., we started to investigate two important fossiliferous sites: Cerro Colorado and Cerro Los Quesos. Within these two areas, measurement of multiple stratigraphic sections combined with extensive field mapping of a number of distinct marker beds was carried out, which allowed a high-resolution correlation and creation of a local lithostratigraphic framework. Integrated tephrostratigraphy, ⁴⁰Ar/³⁹Ar dating and diatom biostratigraphy permitted an accurate chronostratigraphy to be established. Both biostratigraphic and radiometric ages converge to indicate a late Miocene age for the two sites, amending previous attribution of Cerro Colorado and Cerro Los Quesos to the middle Miocene. Age models for the site of Cerro Los Quesos reveal that sedimentation rates are high but in line with those of high-productivity environments, thus invalidating the hypothesis of exceptional sedimentation rates as the main cause for the formation of the Lagerstätte. These results are extremely important also in the perspective of building a complete stratigraphic framework for the Pisco Fm.
The morphology and shallow structure of the Peru continental margin has been mapped using bathymetric and seismic reflection profiles f r om lat 6° S to 16° S. Other geophysical and geologic data are used to constrain interpretations of the margin's deeper structure and to relate the offshore to the onshore Andean geology. Two prominent structural ridges, subparallel to onshore Andean trends, control the distribution of the offshore Cenozoic sedimentary basins. The Coastal Cordillera, which surfaces north of lat 6° Sand south of lat 14°S, can be traced onto the offshore as an Outer Shelf High (OSH); it is evidently cored with Precambrian and Paleozoic metasediments and crystalline rocks. A series of shelf basins is situated between the Coast Range/ OSH and the Andean Cordillera: f r om north to south, these are the Sechura, Salaverry, and East Pisco Basins. A second set of upper-slope basins flanks the Coast Range/OSH to the southwest, limited seaward by an Upper-Slope Ridge (USR) of deformed sediment: from north to south, these are the Trujillo, Lima, and West Pisco Basins. The Yaquina Basin lies within divergent arms of the USR. The shelf and upper-slope basins are set on continental massif. An anastomosing network of elongate ridges and ponded sediments is the surficial expression of the subduction complex, which apparently begins just seaward of the USR. The effect of the late Paleocene/Eocene Andean orogeny has been extrapolated offshore as a distinct interface of seismic velocity in the Salaverry Basin. Though Cenozoic marine sedimentation in the shelf basins did not begin until after this event, sedimentation in the upper-slope Trujillo Basin may have been more continuous through the early Tertiary. In the Trujillo Basin, the bulk of the nearly 4 km thick sedimentary section is of Paleogene age, while in the adjoining upper-slope Lima Basin to the southeast, the bulk of the nearly 2 km thick sedimentary section is of late Miocene or younger age. Apparently, post-Oligocene tectonism caused uplift, deformation, and a gross reduction of sedimentation in the Trujillo Basin; this event is evidenced by boundaries of differential structural deformation in seismic reflection profiles. In middle to late Miocene time, while orogenic activity affected the inland Andean Cordillera, the upper-slope Lima Basin subsided and began its depositional record. Unconformites in shelf basins apparently reflect the inland tectonism at this time. The boundary between the Lima and Trujillo Basins, and between the contrasting styles of upperslope tectonic movement, is near lat 9.5° S, coincident with the present day intersection of the Mendana Fracture Zone with the continental margin. A final phase of upper-slope deformation closed the Pliocene. Like earlier tectonic activity, the major break in structural style of this epoch occurs near lat 9.5° S: compressional faulting and folding characterize the younger sediments of the Trujillo Basin, while the Lima Basin appears as a broad, open syncline, distrubed only in its southernmost occurrence.
A new species of protocetid archaeocete, Eocetus wardii n. sp., is named based on material from the late Lutetian (middle Eocene, 43-44 Ma) Comfort Member of the Castle Hayne Formation, North Carolina. This material includes portions of the skull, thoracic, lumbar and caudal vertebrae, ribs, and the right innominate. The innominate (pelvis exclusive of the sacral vertebrae) has some characters in common with the innominata of other protocetids, including sufficient size to support a weight-bearing hind limb. This suggests that Eocetus wardii was capable of both terrestrial and aquatic locomotion. The innominate also includes some features in common with basilosaurid archaeocetes including a shift in the relative positions of the pubis and obturator foramen. In addition, the bone histology of Eocetus is found to be very different from that of other archaeocetes and sirenians (sea cows and dugongs). The ribs and vertebrae are composed of a central area of trabecular bone enveloped by layers of dense cortical bone. Eocetus has previously only been known from a few specimens from Gebel Mokattam near Cairo, Egypt. This identification makes Eocetus the only protocetid archaeocete genus known from both sides of the Atlantic Ocean.
— We studied sequence variation in 16S rDNA in 204 individuals from 37 populations of the land snail Candidula unifasciata (Poiret 1801) across the core species range in France, Switzerland, and Germany. Phylogeographic, nested clade, and coalescence analyses were used to elucidate the species evolutionary history. The study revealed the presence of two major evolutionary lineages that evolved in separate refuges in southeast France as result of previous fragmentation during the Pleistocene. Applying a recent extension of the nested clade analysis (Templeton 2001), we inferred that range expansions along river valleys in independent corridors to the north led eventually to a secondary contact zone of the major clades around the Geneva Basin. There is evidence supporting the idea that the formation of the secondary contact zone and the colonization of Germany might be postglacial events. The phylogeographic history inferred for C. unifasciata differs from general biogeographic patterns of postglacial colonization previously identified for other taxa, and it might represent a common model for species with restricted dispersal.
New material of Natchitochia from the Bartonian Archusa Marl Member is described here, including thoracic, lumbar, sacral, and caudal vertebrae, an innominate, proximal femur, and pedal? phalanx. The vertebrae and innominate are similar to those of Qaisracetus and Georgiacetus. The structure of the caudal vertebrae support previous observations that as sacral vertebrae disconnect from the sacrum, they become caudalized, developing hemal processes on the posteroventral margins of the bodies, reminiscent of chevron bones associated with true caudal vertebrae. The innominate of Natchitochia shares an elongate ilium and pubis with Qaisracetus and Georgiacetus, which differ from the innominata of the more apomorphic archaeocetes. Comparison of archaeocete innominata and sacra in a phylogenetic context indicates that the apomorphic sacrum composed of 4 vertebrae (Pakicetus, Ambulocetus, Rodhocetus, Maiacetus) was reduced to 3 (Qaisracetus) to 2 (Protocetus?, Natchitochia) to 0 (Georgiacetus, Basilosauridae), while the innominata remained robust, supporting a large hind limb until the origin of the Basilosauridae. In Georgiacetus, the innominate is large but detached from the vertebral column, preventing the use of the hind limb in terrestrial locomotion. More crownward cetaceans for which the innominate is known display greatly reduced innominata and hind limbs are disconnected from the vertebral column.
The family Protocetidae was first delimited to include Protocetus and Eocetus, the only protocetid genera known at that time. Both are from the middle Eocene of Gebel Mokattam, Egypt. Only three genera were added to the family prior to the 1990s, but since then 16 genera from Indo-Pakistan, North and West Africa, and North America have been added, greatly expanding our knowledge of their diversity, anatomy, behavior, and biogeography. Protocetids are as yet unknown from Europe, Oceania, the North Pacific, or Antarctica. Here, several protocetid teeth are described from New Jersey and South Carolina. The New Jersey specimens represent the northern-most discovery of protocetids in the world. Several were collected by avocational paleontologists, while others were identified in museum collections, where they were previously misidentified. Currently, there are four protocetid species from North America, each in its own genus: Carolinacetus gingerichi, Crenatocetus rayi, Georgiacetus vogtlensis, and Natchitochia jonesi.
High-resolution calcareous nannofossil and foraminiferal investigations of the Bidart and Loubieng outcrop sections allow to define a time-calibrated sequence of 47 bio-events within the Danian/Selandian (D/S) boundary interval (61.2–59.7 Ma) of Aquitaine (SW France). The D/S boundary, as originally defined in Denmark (start of clastic sedimentation at the base of the Lellinge Greensand Formation), is marked by the end of the acme of the nannofossil family braarudosphaeraceae. This bio-event, dated at 59.9 Ma, has also been identified at the lithological change from limestone-dominated (Lasseube Formation) to marly sedimentation (Latapy Member of the Pont-Labau Formation) in SW Aquitaine and at the base of the red marls of the Itzurun Formation at Zumaia (Spain), recently designated as Global Stratotype Section and Point (GSSP) for the D/S boundary. This implies contemporaneity of this lithological shift throughout Europe and a GSSP proposal, which is consistent with the original boundary definition. The braarudusphaeraceae-event is believed to be due to the interruption of freshwater influx, probably related to a sudden decrease in precipitation. It is located at the top of nannofossil zone NP4 and within planktonic foraminiferal zone P3b and bracketed between the lowest occurrence (LO) of Morozovella velascoensis (below) and the LO of Fasciculithus tympaniformis (above). It is coincident with the LO of Bomolithus elegans, the LCsO (Cs = consistent) of Fasciculithus janii and the LO of Subbotina velascoensis. The D/S boundary as originally defined is 400 k.y. posterior to a major discontinuity, recorded throughout the Tethyan Realm (Tunisia, Egypt) and up to now erroneously considered to correspond to the D/S boundary. This break in sedimentation, dated at 60.3 Ma and coinciding with the P3a/P3b boundary, is due to a major sea-level fall. It is correlated with sedimentation changes in the Aquitaine–Zumaia area (start of development of marly interbeds) and in the North Sea Basin (transition Bryozoan limestone–Calcisiltite in Denmark; transition shallow marine Mons Formation–continental Hainin Formation in Belgium). The Loubieng section supplements the Zumaia section. Because of its rich and well-preserved fossil content and continuous sedimentation it constitutes an excellent auxiliary section for the D/S boundary.
The central and northern Peruvian margin consists of a series of 8 paired forearc basins which may be separated into an inner set of shelf basins and a seaward set of slope basins. We have examined the Cenozoic stratigraphy of the onshore portions of the Sechura Basin (5–7°S) and Pisco Basin (13–16°S), two shelf basins which have accumulated marine sediment discontinuously since the mid to late Eocene. Cenozoic sediments in the Pisco Basin were deposited during at least three major transgressive cycles. Each sequence is preserved as a similar vertical progression of facies including coarse nearshore bioclastic conglomerates and sandstones grading upwards into sandy siltstones and mudstones, and capped by biogenic deposits including diatomites, diatomaceous mudstones, dolomitic horizons, and phosphate deposits. Stratigraphic nomenclature for the Pisco Basin has recently evolved; a stratigraphy presented here includes the Eocene Caballas Fm., upper Eocene Los Choros fm., upper Eocene to lowermost Oligocene Yumaque fm., uppermost Oligocene to middle Miocene Chilcatay fm., and upper Miocene to Pliocene Pisco Fm. Major hiatuses in the Pisco Basin span the Late Cretaceous to middle Eocene, early to late Oligocene, middle Miocene, and late Pliocene/Pleistocene to Recent. Cenozoic sediments of the Sechura Basin were deposited within at least 4 major transgressive cycles with hiatuses during the Paleocene to middle Eocene, Oligocene, early to middle Miocene, and late Miocene. Based on recent biostratigraphic studies, sediments enriched in biogenic components accumulated between about 40-36 Ma, 24-16 Ma, and 11-3 Ma in the Pisco Basin and between 40-37 Ma and 8.5-4.5 Ma in the Sechura Basin. In both basins, the most diatomaceous sediments are restricted to the Late Eocene and Late Miocene through Pliocene. The temporal distribution of biogenic sediments suggests that high productivity conditions linked to coastal upwelling have occurred episodically since at least the Late Eocene. The occurrence of diatomites and phosphorites is diachronous between the Pisco and Sechura Basins and between the Peruvian forearc and other circum-Pacific Monterey Formation analogs, a reflection of the strong influence of local tectonism on sedimentation patterns. The volume of Neogene sediments along the Peruvian forearc is nearly twice that of the Monterey Fm.; despite basin-to-basin facies diachroneity, these deposits very likely contributed to fluctuations of the late Miocene carbon/CO2 system by acting as large carbon sinks.
A newly identified early Oligocene marine transgression across the Pisco Basin of southern Peru resulted in the deposition of at least 150m of fossiliferous sandstones and siltstones, informally designated the Otuma formation. Basal sandstones can usually be recognized in the field by the presence of the gastropod, Turritella woodsiLisson 1925. New stratigraphic data demonstrate that Cenozoic marine sediments were deposited in the Pisco Basin between about 41-34 Ma, 31-28 Ma, 25-16 Ma, 15-11 Ma, 10-5 Ma, and 4-2 Ma. Most sequence boundaries in the Pisco Basin coincide with compressional tectonic events and/or eustatic low stands of sea level.
Whales are first found in the fossil record approximately 52.5 million years ago (Mya) during the early Eocene in Indo-Pakistan. Our knowledge of early and middle Eocene whales has increased dramatically during the past three decades to the point where hypotheses of whale origins can be supported with a great deal of evidence from paleontology, anatomy, stratigraphy, and molecular biology. Fossils also provide preserved evidence of behavior and habitats, allowing the reconstruction of the modes of life of these semiaquatic animals during their transition from land to sea. Modern whales originated from ancient whales at or near the Eocene/Oligocene boundary, approxi-mately 33.7 Mya. During the Oligocene, ancient whales coexisted with early baleen whales and early toothed whales. By the end of the Miocene, most modern families had originated, and most archaic forms had gone extinct. Whale diversity peaked in the late middle Miocene and fell thereafter toward the Recent, yielding our depauperate modern whale fauna.
In order to gain insight into the functional properties of the tail in North American beavers (Castor canadensis) we (1) examined morphological features of skeletal, muscular, vascular, cutaneous and neural structures; (2) determined the segmental organization of spinal roots and certain stimulus-response features of receptive fields of single dorsal root fibers; (3) mapped the main somatic sensory area (SI) of the cerebral neocortex, and (4) attempted to relate these findings to observations of tail behavior in living beavers. The behavioral observations revealed the beaver capable of forceful yet discrete movements of the tail in water. A morphological correlate of these motor skills was the distinct segmentally organized pattern of serial muscle tendon arrangements and spinal sensory and motor innervation. Neither the receptors innervating the scales or hairs of the tail, the stimulus-response properties of single dorsal root afferents, nor the representation of the tail in SI suggested unusual cutaneous sensory capabilities associated with the morphological and behavioral specializations exhibited by the beaver's tail.
Biozonation and biochronology of Paleogene calcareous nannofossils from low and middle latitudes
- C Agnini
- E Fornaciari
- I Raffi
- R Catanzariti
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First remingtonocetid archaeocete (Mammalia, Cetacea) from the middle Eocene of Egypt with implications for biogeography and locomotion in early cetacean evolution
- R M Bebej
- I S Zalmout
- Abed El-Aziz
- A A Antar
- M S M Gingerich
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Gingerich, P.D. (2016). First remingtonocetid archaeocete (Mammalia,
Cetacea) from the middle Eocene of Egypt with implications for biogeography and locomotion in early cetacean evolution. J. Paleontol. 89,
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Postcranial osteology of the North American middle Eocene protocetid Georgiacetus
- Hulbert
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Eocene stratigraphy and depositional history near Puerto Caballas
- T J Devries
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